But what is that red line?Slipstream should be a thing by then... so explore new areas of the galaxy. They could easily come back home and follow up on established species, just as TNG did with the Klingons, Romulans, etc. Don't put in things that unnecessarily cross the red lines of established fans. If you want to follow up a prior episode, don't make it a mystery box and instead put it in a "last time on Star Trek..." segment before the opening teaser.
No one has that answer. Yes, TNG did it well, but the way it is described now is "don't go anywhere new" and I'm firmly opposed to that. I am far more interested in checking with Klingons after you establish something new.
Having had several casuals or nonfans in my life and family I can say that many people treat it that way, and don't want to get in to the franchise because of it.Some people here act like every prior episode in Star Trek's what 600+ episode history has the density of THE X-FILES mythology. If Legacy would be the Next Next Generation, what could a Next Next Next Generation be, set in the say 2460's to put it 200 years post TOS and 80ish years post TNG/DS9/VGR midpoint?