I think it should be retained as the clear convention of the early Church it was. More and more people began to be the 'saints' of God in the great in-gathering of the Gentiles, and so it became a great way to invite people to become God's 'holy ones'—when you are a Christian, you are and have the potential of more truly being 'God's holy ones.'
I can't remember which of the Church Fathers it was, but they said that 'saints' as a term for even Christians on earth fell out of use pretty early, and was reserved only for the 'church triumphant' or, the saints in heaven. Rightly and naturally so, for the saints in heaven are definitionally saints, and are in heaven, and are those "righteous made perfect," (Heb 12:23) whereas the rest of Christians are "called to be saints," (1 Cor 1:2) and are to continue to "strive for peace with all men: and holiness, without which none shall see the Lord" (Heb 12:14), and are counseled by the Apostle: "But according to him that hath called you, who is holy, be you also in all manner of conversation holy: Because it is written: You shall be holy, for I am holy. And if you invoke as Father him who, without respect of persons, judgeth according to every one's work: converse in fear during the time of your sojourning here" (1 Pt 1:15-17).
One thing people also neglect is that the class of saints in heaven was a relative novelty at the time of the New Testament: Christ had only opened heaven to the spirits detained in the spiritual prison of the Bosom of Abraham, and brought them to glory at His entrance into heaven.
So saints being anything other than God's people on earth (at least as to be being called saints) was something quite new.
There are is a of looking at the convention of calling all Christians saints in a non-technical way as still relevant (and they can co-exist, the technical canonized term 'saint' and the term 'saints' as applied to Christians on earth), such as that it can be seen as an appellation of endearment: God's people are His set-apart people (the very essence of the word 'holy') no matter where they are; even if there is disparity in the completion of their sanctification, and degree of perfection.
One argument that could be made against it is that there are many, many tares among the wheat (a Scriptural reference to false Christians in the Church), and no one can know who is one of God's elect just by looking at them, and so it is safer to view Christians in light of their calling to be saints, rather than all being, equally, every one, saints.