The only way to determine whether this event has already taken place or whether it is still future is to work out whether Revelation 11:1-2 speaks of a literal or a figurative temple/courtyard. It may even be needed, thereafter, to consider the possibility of this outer courtyard exemption having started with Christ's ascension and continuing right until he returns.
Because verse 1 starts with "And there was given me a reed like unto a rod", this is a continuation of what was said before, about the prophetic ministry John was given, which started with him eating a little book that tasted sweet as honey in his mouth but which then made his belly bitter. After he'd done that, he was given that measuring reed. Was his eating of the little scroll from the angel literal? Of course not! Then why would anyone think the measuring, or the courts, would be literal?
However, this should remind us of an Old Testament section where the prophet Ezekiel was given a vision of God's city where a man who appeared as brass (brass standing for God's judgment) had a measuring reed with which to do much measuring, including an inner and outer court. It was all about the abominations of the house of Israel, even inside the temple, and God's coming judgment (chapter 44). Here is an explanation of the significant connection between Ezekiel and John's respective visions, first re. Rev. 11:1:
"This is a figure taken from Ezekiel 40:5, where the prophet sees a
measuring reed... with this the measurements are taken of the mystical
temple of Ezekiel chapters 40 to 43.. 'In the man's hand a measuring
reed of six six cubits long by the cubit and an hand breadth.' Now,
three palms of the hand measured one span. And two spans equalled one
cubit. Therefore six palms of an hand measured one cubit. But the
measurement of the mystical temple was not according to that cubit.
The wording is this, Ezekiel 40:5, 'a measuring reed of six cubits by
the cubit and an hand breadth.'
That means that the reed was not merely six cubits - which was the
measure of an earthly man - because to each of the six cubits was
added an hand's breadth... six hand's breadth equalled one cubit. Then six cubits of a cubit and an hand's breadth actually amounted
to seven cubits. Perfect measurement. The measure of the perfect
Man, that is, the heavenly Man, which is Christ. By this measure the
mystical temple is to be measured.
This is the measure of conformity to the image of Christ, Rom. 8:29,
not only individually, but of all such individuals corporately united:
it is the temple that is to be measured. 'All the building fitly
framed together groweth unto an holy temple in the Lord: in whom ye' -
plural - 'are builded together for an habitation of God through the
Spirit.' Eph. 2:21,22.
Therefore, spiritually, the temple is no structure of stone, mortar,
or wood. It is the inward habitation of God; Father, Son, and Holy
Ghost, dwelling within the unity of the saints separated from the
world and gathered together in the Spirit.
This appears in Eph. 4:13 concerning the edifying of the body of
Christ, 'till we all come in the unity of the faith, and of the
knowledge of the Son of God, unto a perfect man, unto the measure of
the stature of the fulness of Christ.' Where his fulness, dwelling
in the interior of the temple, that is, the saints gathered in unity,
transforms the whole living company into his own likeness.
Not only is John given a book to eat, but also a reed to measure. The
one is to the nations; the other is for the temple. He is not to
measure the outer court, for that is to be trodden under foot of the
Gentiles for forty and two months, the same period in which the two
witnesses are to prophesy...
The reed represents the prophet's ability... to measure what is of God
on earth at a given time, as opposed to what is merely supposed to be
of God on earth at that time. This figure cannot possibly be confined
to John, any more than the temple can be limited to the apostles'
lifetime. Both these figures signify principles which can and must
apply throughout the age... till the day of judgment.
...This measures where his presence dwells... The altar was the
place where sin was condemned in the flesh and put away by the
offering up of the body of Jesus once and for all. This becomes the
measure. Nothing of the flesh is tolerated past the altar, which is at
the threshold of the house...
The flesh - if not constantly kept mortified by the Spirit - will seek
to claim the altar, and enter in some other way, setting up its own
measurements, pretending to experiences to which it is foreign,
assuming a false spirituality, tending strange fire... avoiding the
man with the measuring rod." The Revelation of Jesus Christ, pp
251-255, John Metcalfe
Without grasping what verse 1 means, verse 2 will be in limbo. What is to be measured, and with what, determines the meaning of verse 2, which is what is being asked about. Now that the inner court and its symbolic measurement has been explained, it is easy to see what casting out the outer court means, and how that started to happen at Christ's ascension, continuing to this day. The explanation you seek follows::
"Now, to apply the figure of the temple, the entire temple,
precincts, outer court, the whole, answered to the measure of the
stature of the fulness of Christ in those wonderful early days of the
ecclesia, the fulfilment of the type of the temple. The whole of the house of God was thronged with sons. The visible church in its
entirety answered to the indwelling of Father, Son and Holy Ghost, and
included all that could be measured with the measure of Christ.
But the Act of the Apostles is not Revelation, the last book to be
written. By then the apostasy had begun to work... when 'they will not
endure sound doctrine; but after their own lusts shall they heap to
themselves teachers, having itching ears; and they shall turn away
their ears from the truth, and shall be turned unto fables', II Tim.
4:3,4. This is outer court religion. This spread apace." (Ibid.
p 257-8)
Those false teachers went out from the ecclesia - into the outer court - 'that they might be made manifest that they were not all of us', I John 2:19. So Jude confirms, "These be they who separate themselves" - from the apostles' doctrine and fellowship - "sensual, having not the Spirit" Jude vs. 19.
"The outer court presents an external, visible profession of
Christianity - precisely because it is the outer court; the thing seen
first, the thing most conspicuous - having the form of godliness but
denying the power thereof. Visible, because one cannot see inside the
shrine, but one can enter and survey the court. This is the outward
form of Christendom... In the outer court gathers a flock of goats
bleating, 'Lord, Lord' and appearing to mean each word of it. Here are
the workers of miracles; the casters out of demons; the sounding brass
of a babel of tongues; in a word, the gifts without the Giver."
(Ibid. pp 258-9)
The symbolism of the forty-two months is then mentioned (for it is not literal either). It speaks of the duration of the testimony of God's two witnesses, which appears again and again through the age. Revelation 11:3 has God sending them to show up publicly the take-over of the professing church by rotten outer-court religion. God's prophetic word judges mere profession devoid of the indwelling Holy Spirit. This measuring of true holiness (found in those allowed into the inner court) means that unholiness is cast out into the outer court. Ezekiel spoke of that symbolic measuring and judging of God in his day; John was given the vision that started with the beginning of the holy ecclesia on that Day of Pentecost, to continue till Christ returns. The outer court of unholy religiosity is truly crowded now.
So the answer is, it is not literal but spiritual measure, according to the measure of Christ, which started at the birth of Christ's Church at Pentecost, to continue till Christ returns.