DC is now in a completely unwinnable situation when it comes to Batman.
If Reeves decided that his vision didn't work out with whatever then it's probably for the best that he wasn't forced to put his Batman on this universe, but now DC Studios is in a ridiculously complicated situation when it comes to the character.
Here are the options I see for them going forward:
1. Use the Jokerverse as the starting point for the new Batman. As much as Todd Phillips like to posture himself as this pretty well defined creative auteur or whatever it's pretty clear he's not and he's actually a bit of a hack even though I loved the Joker movie. And if Joker 2 does well, then it's inevitable we'll one day see a Batman of that universe (especially since Phillips said he wants to see what a Batman of that universe would look like:
Todd Phillips Wants to See a 'Batman' Movie from His 'Joker' World - Variety ) so you might as well just use that Batman. I can see him and Gunn sharing similar sensibilities so I don't think it's that out of the realm of possibility.
2. Create an entirely new Batman for the DCU and give him a solo AFTER Reeves is done. The earliest that a JL film could come out is in 2028 anyway which is around the same time that the Reeves trilogy would be done so that's not much of a problem. But then you run into a bigger issue which is: Who in the actual hell will want to take on the job of directing Batman under those circumstances? Not only would that director have to immediately be following up a Batman centric connected universe that lasted for a decade, but they'd also have to reinvent the character enough it's distinctive from the Reeves version while at the same time making sure it connects to the wider DCU and whatever Gunn has already established. This new Batman will be
completely unable to attract a talent on the caliber of Christopher Nolan or Matt Reeves so it'd immediately be a downgrade unless maybe Gunn himself directs it.