Many players are not into this game for the combat at all. They want to trade, explore, do some mining, missions etc. That is not necessarily doing the same thing over and over. And even if it was doing the same thing over and over... that would be their prerogative. Who am I to say what other ED players should be doing in this huge universe?
I love the combat myself, but the strength of the ED gameworld is that players can seek out combat if they want it. They can choose what they want to do.
Dedicating the entire human bubble to alien warfare will severely limit the options for a large part of the players who do not want combat at all. They certainly wouldn't want to be forced into a tedious migration to the second bubble.
Part of the bubble, even a significant part, might become a warzone. I think that would be fine.
I do not think we will see the entire bubble appropriated for this kind of gameplay though, because that would force players to "do the same thing over and over again", namely combat.
Only a minority might want that, a very small one. FDev knows that better than anyone.
I hope that a few hundred systems will become part of a battle zone and that on the edges of that zone a lot of profit can be made for traders of all kind, but with the added risk of encountering Thargoid ships. Perhaps the Thargoids will scan ships and only attack if there are military goods, f.e. weapons, on board, or if the transporting ships themselves are armed.
There could be a few planets deep in the war zone that have not been touched by the Thargoids for reasons unknown to us humans and doing business there could be very lucrative, but to travel there might be very dangerous.
With a setup like that there is something for everyone. People can look for combat by going into the warzone. Traders who like to live on the edge for high profits can seek it out and those who do not want this can stay in parts of the bubble that are safe.
An approach like this will be entirely in keeping with the nature of Elite: People will be able to choose what they want to do.