I'd like a map expansion but here's why I think it won't happen.
Presumably R* are working on VI, and will be putting all their 3D modelling resource into that. With RDR out this year, it's hard to see them bringing out VI before 2020. That will make the current map 7 years old at least.
Obviously in that time graphics are going to take a big step forward. Its not going to be viable to plonk a UHD island next to a HD one without it looking, well, crap. There are two options - you either create a new city with 2013 graphics and add that, Erm... Nope. Or you give the whole of Los Santos a very time consuming remastering job.
It feels like the obvious choice is just to start again in VI with a brand new map. That's been a winning formula for so long, and just based on the first month of sales, they'd have to be very bold to move away from that.
I'll grant it is a difficult conundrum. The current player base makes them money and they won't want to disrupt that. But it's difficult to see how they viably expand GTA V's online without a lot of expense for uncertain benefit, versus the alternative of starting afresh with GTA VI.
^^ Yeah, a ton of detail work goes into a brand new map--model creation, layout, checking for potential wall glitches, etc. I doubt a new map is in the works other than for a "GTA Online v2" or GTA 6.
But(!) if more staff are back working on GTA Online, there's a lot R* could quite easily do to the existing map to dramatically improve it.
I've posted about this so many times... just bring to life those otherwise unused elements in-game that would add the following game play:
* More variety of ways to lose four- and five-star wanted levels, especially up north where cover is pretty scarce. I've noticed that R* recently reduced the amount of time it takes to lose the LSPD at certain levels--a welcome change!
* Extend waterways into the mainland so that all manner of watercraft can interact with at least some mainland action; though would have to be done carefully so that it doesn't interfere with existing heists or contact missions. Without access, watercraft are otherwise completely useless to most in-game activity. The added islands and oil rigs idea is a good one--and make better use of existing islands somehow (and how about opening up the lighthouse?)
* Much faster surface and below-surface watercraft with armor and decent weaponry that allow players to battle it out fairly with the water-based LSPD (rarely seen in-game!) and PvP. Add some CEO work that's best suited for watercraft to encourage it. And tone down the waves so that players can actually aim and get to destinations faster--definitely needs tweaking.
* More connecting mine shafts, covered water ways (like the one at Del Perro) and some new things to explore/use, like underwater tunnel entrances (we have rebreathers and scuba gear, the Stromberg, etc.) and areas/buildings only accessible via water entrance--Watch Dogs has this, and it works well.
* Open up more interiors so that existing things like the Gas mask and new items like Smoke grenades and Flash bangs can be put to good use against the LSPD and other players (interior game play).
* How about some well-placed zip lines in Los Santos and up north? We can rappel...zip lines (e.g. top of building to tunnel entrance) could make for some great variety/evasion.
To Rockstar's credit, the Thruster has already "unlocked" new game play just by nature of new places you can now easily access (e.g. "Executive Search" is now a whole different ball game just because of where the Thruster can go, allowing players access to cool new areas):