Apologies for the late reply. Something hit me just now.
I think the success of The Orville may have a lot to do with Picard going forwards. TNG fans just go gaga over the series, showing that TNG is no in the realm of forgiving nostalgia.
I think that's only half of it. I think there were a lot of people looking forward to a new Star Trek series and then there were many who didn't like that it would be another prequel. "We want to go passed
Nemesis!", they would exclaim. So Alex Kurtzman must've been aware of the sentiment. But that wouldn't mean he'd know what to do with it.
Then the other half kicks in. He saw the response to
The Orville, then decided he'd make this Post-
Nemesis series about Picard. Except Patrick Stewart didn't want to play Picard anymore. So Alex Kurtzman buttered him up and agreed to make Picard different, so Sir Patrick wouldn't feel like he was playing the same character exactly the same way again. They just used what happened last we saw and heard anything of the 24th Century as a springboard (
Nemesis and the 2009 film respectively) to drive Picard into this changed direction and went from there.
Throw Michael Chabon into the mix, the writer of "Calypso" who's also a critically acclaimed author, and people already excited know they have an A-lister as the showrunner.
So they had their setting, their main character, their actor, their premise, and the main writer all locked into place. That's how I think it came together.
EDIT: I think the Borg came into the picture because that's the enemy most associated with TNG. Since the Romulans were already going to figure prominently in
Picard, if they were using
Nemesis and 2009 as a springboard, they probably wanted to figure out how to tie the Romulans and the Borg together.
And since the Borg are a form of artificial intelligence, they can tie that in somehow to Data. In turn, they would also have an opening to include Seven of Nine, the most popular character from
Voyager. Jeri Ryan didn't want to appear in
Nemesis because there was no natural connection. But in
Picard, there would be.
So they started off with this one thing and as it grew and grew and grew, it all fell right into place.