Mission Pass Season 15 ends on 27/28 April. Exactly four weeks after that is 25/26 May so this coincides with the end of a probable Season 16. JP are ending Mission Pass on PSO2 so it seems reasonable to expect Global will be as well. If so we may also surmise that Tier Missions are going to be deactivated and permanently greyed out as Limited-Time Missions usually are.
Whether this is to make way for a New Genesis Mission Pass or another content mechanism is a little unclear; I do think it'd be a bit much for New Genesis to be without Mission Pass, FUN Scratch or a new replacement since they are free or freemium offerings that give much of the game's activity and content-earning routes for F2P or subscription-style players.
On the Global side particularly the loss of these without a replacement would come as a bit of a pacing shock alongside the conclusion of the content rush we've been in for around a year now. We don't want Global players reviewing New Genesis negatively in the weeks following its release by saying there's nothing to do!
But this has just been announced. I'm sure they have regular activities and a persistent gameplay loop planned for New Genesis and it makes sense to hold that back to include it as part of the pre-release hype they should be doing, just as it makes sense to announce the termination of Gold Ticket items ASAP to prevent people buying them unnecessarily. It's just unfortunate that two sensible related actions cause concern for existing players.
The bigger question is what happens to a lot of content that will now become permanently unavailable, with revivals in Mission Pass itself no longer possible. This is particularly troublesome for Global as our Mission Pass focused on cosmetics far more than JP and with items that were not only tradable on JP but several of which have recently returned in a permanent Weapons Badge exchange.
Obviously I'd like to see all items get switched over to being tradable and either added to the same permanent sources as JP enjoys or a permanent Mission Badge exchange with Mission Badges being rolled into regular PSO2 gameplay loop rewards (the simplest methods being to make them regular uncommon drops or available by exchanging another permanent token item like EX-Cubes). This would finally, finally, end several PC players' issues with never having been able to get certain items from Seasons 1-3 too.
Most importantly, whatever this paves the way for when it comes to New Genesis content, it also provides a golden opportunity for JP and Global to get it in the same form with no more splitting of where content comes from and whether it is tradable. I'm really hopeful this is the case because "JP have this item easier/cheaper/better than us!" is a complaint that always hurts to see and it's be peachy if it wasn't a thing in New Genesis.