Well, clearly Star Trek Legacy needs to happen now, otherwise this pile on will quickly run out of new material.
Imagine... you could have a YouTube hate click channel denouncing a series for following canon too much, being tonally consistent with what came before, having great Star Trek music, bringing back many more Berman Trek production design people, maybe even someone like Ira Steven Behr comes back to write an episode, storylines that deserve follow-ups and some serialization get covered... the horror, the horror!
Legacy's going to be
Picard Season 4 without Picard, if it happens. The difference between
Legacy and
Picard is that they'd flesh out the Enterprise-G crew, introduce some new characters, and follow-up on whatever Terry didn't get to during PIC S2 and S3 that he would've wanted to do if he had more episodes or seasons to work with.
If not for Patrick Stewart himself, I'm sure
Picard would've gone on to a fourth season and beyond. Under different circumstances, that weren't very specific to
Picard, I think it would've run for as long as
Discovery is and as long as I assume
Strange New Worlds will.
I don't think Ira Steven Behr would work on
Legacy under Terry Matalas. It would be like a demotion for him. I think, to get Ira Steven Behr back, or Ron Moore for that matter, you'd have to offer them a series of their own. Ira Steven Behr doesn't care about following up on TNG or VOY. He cares about following up on DS9. To the point where they came up with a hypothetical eighth season on the special,
What We Left Behind. If they were doing a DS9 follow-up series, specific to DS9, Ira would be my first choice all the way. On
Picard and presumably
Legacy the pecking order is that TNG comes first, VOY comes second, and DS9 comes a distant third. They're more likely to do follow-ups to VOY than DS9. Especially with Seven of Nine as Captain and if the Delta Quadrant becomes something they can easily reach through faster propulsion.
At some point, I don't remember where, Terry mentioned the Klingons. I think he'd have it so something changed with the situation with the Klingons in the 25+ years since we've last seen them in the live-action 24th Century, besides Worf, so nothing from the end of DS9 would still apply. Martok would be out of the picture and they'd be long-recovered from the Dominion War (which Sloan said would only take the Klingons 10 years to recover from anyway). What seemed to happen with
Picard was the writers would look at "All Good Things" to see how much of that future was still workable for them to use. Picard at the Vineyard, having an on-again/off-again romance with Beverly, the Enterprise-D is back, Geordi and his kids, Data back, looking older, and having emotion, the Neutral Zone no longer existing, etc. They're not bound by "All Good Things", and they don't follow it exactly (in some places they can't!), but it does seem to be their starting point for inspiration.
EDITED TO ADD: I'd like to see what
Legacy could do further with the Romulan Free State. Especially since SNW seems to be honoring "Balance of Terror" and probably won't use them. The Romulans have, over time, become more associated with TNG than TOS anyway, and
Picard Season 1 brought a lot to the table with them.