Do you think developers will consider the idea of being able to explore other galaxies? Perhaps with an expansion that adds new FTL technologies can cover long distances between one galaxy and the next. These technologies will be available after at least 300 years game, only that these engines will be installed in the Titan-class ships (Warfare Expansion?) Because of the enormous amount of energy they require. It will be a one way travel seen that once you get the engines will be unusable, so if you're lucky you can establish yourself in a living planet that are in the system in which arrivals, or you will be forced to sacrifice your ship to build a space habitat. Then you will have to deal with other species that meet ... This phase I see it more as a New game + mode, just do not start again but continues the same.
Actually simulating two galaxie would be impossible from a technical point:
The game is a native x32 application. Wich means it is restricte to 4 GiB of RAM. While not a performance issue with the galaxies we have right now, it would be a huge issue if you wanted to simulate twice the number of stars. And as Clausewitz is a game engine, just switching th x64 would be far from trivial. If they want to do it, they have propably been working on it for years now.
As a Game+ Option:
That might be viable. Actually there is a long history of converters where one games state was turned into another games map:
https://forum.paradoxplaza.com/forum/index.php?threads/paradox-game-converters.743404/
CK 2 to EU 3 and EU 3 to Vic 2 was the longest chain you could string.
With it's galactic scale Stellaris might be the first Pradox Game that can add that natively.
There was a similar scenario in the Original Sword of the Stars.
Hungry Children, where the hivers started with a huge fleet.
Star Drive 2 had this added in 1.1: "New Race Customization Options! These are “Game-Changers” to provide some more unique challenges for you.
– Titan Quest: You begin the game with Titan Construction technology but can ONLY build Titan class military vessels
– Total War: You cannot build colony ships. This should be a fun challenge.
– Newcomer: Your empire was late to the StarDrive party. Other empires start with two additional colonies in nearby systems"
- Newcomer could be simulated with just giving every AI adanced starts.
- Titan Quest could maybe be done via Civic that can not be removed. However one part of the chalenge was that at least 50% of the slots must be filled for a SD ship to be viable. And build time was based on total cost like in Civ. So it might not translate that well to Stellaris.
- Total War could be made an archeivement of sorts. "Do not colonise with your primary species". Would help to have non-adaptive with that.
OP Note:
I guess a lot of the disaprooval comes from the titel. If you named it a Game+ Option/starting option it might work better.