Getting a little ahead of myself here, but...
What'd be cool going forward after this game releases and between the likely-giant timespan between this and GTAVII... would be a couple of smaller, more dense story-driven titles built on the newer engine and revisiting Niko Bellic in Liberty City, for eg. "Grand Theft Auto Revisited: Bellic's Liberty" & revisiting CJ in the original San Andreas, for eg. "Grand Theft Auto Revisited: City Of Saints".
The maps could be totally rebuilt in the new engine and brought up to par; and the time period in each could maybe be ~10yrs or so after the original games -- not so much an epic tale, but more of a steady "drop-in, experience the characters, how they've evolved, experience the worlds again, then drop out" kinda thing.
This would satisfy fans of single player, story-driven content while the new GTA Online is well underway satisfying the multiplayer folks. These could be sold as large DLC expansions or standalone games at a somewhat reduced price (not too much of course, this is an R* game..).
Of course, to further incentivise R*/T2 and make it more of a viable, attractive investment to rebuild these maps/worlds/assets; they could then be updated to current times; and ported into the new GTA: Online as flight/travel destinations. Resulting in an expanded new GTAO that includes Leonida, Liberty City & San Andreas all seamlessly integrated (perhaps San Andreas could be expanded for the GTAO version with a hybrid of the San Andreas/GTAV versions of Los Santos somehow integrated and wrangled together).
EDIT: Additional possibilities: the new Vice City area of Leonida in GTAVI could be redressed for the late 80s/early 90s and we could revisit Tommy Vercetti in "Grand Theft Auto Revisited: Magic City" & the aforementioned recreation of Liberty City could be redressed for Claude to be revisited some time after GTAIII in "Grand Theft Auto Revisited: Ghosts Of Liberty City".
That's four focused single player, story-driven titles that would draw $40-50 a pop for R*/T2 while using some existing assets as a base or helping create lots of assets for Online. Drop one every two years on PS6 alongside a port of GTAVI & GTAO early on = $$$ + Happy Customers
Then GTAVII -- probably arriving on PS7 -- could be more of a major break from the norm and something fresh.
Something like:
GTAVI - Feb '25 (PS5/XS)
GTAO2 - May '25 (PS5/XS)
GTAVI + GTAO2 - Mar '26 (PC)
GTAVI + GTAO2 - Q4 '28 (PS6/X5)
GTAR: Magic City - Q2' 29 (PS6/X5/PC)
GTAR: City Of Saints - Q2' 31 (PS6/X5/PC)
+ San Andreas added to GTAO2
GTAR: Ghosts Of Liberty City - Q2' 33 (PS6/X5/PC)
+ Liberty City added to GTAO2
GTAR: Bellic's Liberty - Q2' 35 (PS6/X5/PC)
GTAVI + GTAR Collection + GTAO2 - Q2 '36 (PS7/X..?)
GTAVII - Q1 '39 (PS7/X..?)