This is one of those passages that I find easier to express in a language that uses subjunctive verbs more regularly & consistently than does English (English has subjunctive, but it is neither particularly common nor very rigidly enforced).
In Spanish, the relevant portion of the passage reads:
para que en todo tenga la preeminencia (Reina Valera)
Literally: "for that in all He may have the preeminence".
"Para que" indicates a dependency, much as the Greek conjunction ἵνα does -- what came before made or will make possible what came next. The "uncertainty" conveyed by the subjunctive need not indicate that the consequent hasn't happened, merely that the consequent was dependent upon something else.
The Greek verb γένηται ("genetai", "might be") is subjunctive; it is also in the aorist tense--it speaks of the past (either it happened in the past or it began in the past).
So if we wanted to be wordy we could render this passage:
"Jesus is [list of attributes/roles, including] He is is the first born of the dead, so that He could be preeminent in every way".
Said another way, if Jesus had not been the first to rise from the dead, resurrection would be a matter in which He was not pre-eminent.
The overall message is consistent with Paul's theology elsewhere. In the context of the resurrection (a gift that has been given by Jesus, even if not everyone has received it yet):
26 The last enemy that shall be destroyed is death.
27 For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him. (1 Cor. 15:26-27)
Conquering death is part of Jesus overcoming all things; this would be closer to option B in the OP. But this is not to say Jesus was not pre-eminent before the resurrection--He was pre-eminent in nearly ever way, but prior to the resurrection He was not yet pre-eminent in rising from the dead.
For thousands of years prophets looked upon that as a certain promise yet to be fulfilled; now we look back upon it as a promise that certainly has been fulfilled.