Speaking personally, I plan to skip Crossbell for now and just play CS3 and maybe CS4, until geofront do their thing or otherwise Crossbell ends up in a good state.
I'm sure that ideally, I should have played Crossbell, and there will be character arcs that continue in CS3 and 4, and that maybe some Crossbell lore will be relevant, and all that jazz. But equally, I personally think I'm capable of getting the gist even if it's not the full emotional context. It's not like Rean has played Zero off screen or anything, there will for the most part be context clues I can work with. And heck, if I misunderstand something that isn't relevant to CS, that could make Crossbell more interesting.
But basically, I'd rather mostly enjoy the CS games now and fully appreciate them later after playing Crossbell properly, than completely ruin the Crossbell games just so I can understand what a Crossbell character means when they say "Oh that reminds me of this thing that happened in another game".