Unexpectedly (upsetting somebody, perhaps), this answer will be completely away of the domain of modal logic or statement analytics; rather, it will be existential. The thing is that in the OP question itself there was no requirement that an answer should come from some specific branch of philosophy.
Sartre claimed that possibility (or opportunity) of an entity or event is always my (rain's probability today is my possibility to get wet or not) and that it is what initially introduces time in my reality here: possibility temporalizes me. The time I'm speaking is primeval or pre-reflective time and should not be confused with psychological or "physical" time which appears as a special time-object later, upon reflection having come into play.
Whereas psychological time is graded into chunks (into before a landmark and after a landmark where a landmark is some thing or event, obstacle or facilitator coming from world) primeval time is smooth. It connects me with the future (which is my state alongside with the possibility realized) without any kind of glue such as promise/guarantee or resources/facilitators - as if the possibility has already come true. Simultaneously, it perfectly detaches me from the above possibility realization without any chronology/postponing or shortages/obstacles. I'm thus fully connected and fully separated at once from the aim which is my possibility, in pre-reflective mode. This seeming contradiction is at the core of human conscious nature because it is based on pure negation. A citation from another local answer:
There is nothing (no anything) that separates the Venus as it appears
from its identity of Venus armless, yet it is not equal to it.
Simultaneously, there is that same nothing that separates it from the
possibility of armness, yet having arms is not any guaranteed, even
not under consideration. (Nothingness does separates by no miles or
millimeters, and it does link by no bridges or molecules.)
Possibility realization is in the future (possibility brings in future by temporalizing me), but that future is "around me", it is here already with me in its final perfect sense - but is in pure inaccessibility. From this point of view,
So that whatever will be possible is possible now
is indeed so. It is surely possible to happen now while it won't. I exist - ever immortal [Ftn.] - right in the form of that future which makes the (meaning of the) "now" and which is out of access.
What is possible is necessary because possibility of something is my future that has been freely chosen by the consciousness, and also because it has not yet come true nor is guaranteed to come. In temporalization, "is possible" and "will be possible" are indistinguishable.
But in reflection, we deal with psychologic or wordly time that is tiled with events like necklace is. Psychologic future is actually always past future ("future in the past", one is tempted to put). When we plan to reach an aim, we reflect on doings, obstacles, resources and order, all of which are objects we process in knowledge; but knowledge (as opposed to intuitive apprehension) is always past. That is why in our dreaming/planning of the future possibility it has the taste of not actual or desirable/scary anymore. We need reflection to plan, yet reflected dream of the future possibility is nothing more than reminiscence of the now "dead" possibility, possibility which is no more necessary despite we may claim we are interested in it. In that profane time "is possible" inertly precedes "will be possible" and both are seen (treated) as occured already: it is future-modal facts (facts cannot be necessary or needed, they simply are there).
Ftn. In Sartre's novel Reprieve, there are several outstanding pages towards the end of the book describing Mathieu's opening to himself that he is free and is an everlasting immortal moment, which is, like light skimming the beach, could never be buried by this sand and stones and is always to be an exile from them all.
Addition. Note that for Sartre, my death cannot be my possibility (for Heidegger, it can and is). My death is a destiny which is always on the side of worlds contingencies and not my freedom; we - for ourselves - are devoid of destiny because we are free, and when sometimes we look at ourselves as at somebody having destiny that means we are seeing currently ourselves as others, or even as things, i.e. living objects which are amenable to outer contingencies. Freedom is amenable only to inner spontaneousness (while in specific conditions, though). Although it is possible to suppose own death, this is not real expectation but rather an apprehension like that the train will arrive late or an icicle will hit my head - the butt in my possibilities, and not my possibilities themselves. So, it is easy to imagine, lying on the sofa, "my death is possible" or "my death will be possible", given that - what I've said in the body of the answer - both events already happened and, to add, happened not with very me. (Dying process can really be my possibility, but dying is a mode of living or life project yet.)
