They aren't going to confine Lobo to Elseworld movies. If he's doing both, its likely that his Aquaman would still be set in the old DCEU while he also plays Lobo for the new DCU.
Yeah I've always figured that was gonna be the case.
Aquaman was WB's highest grossing film. Even if they are going to hard reboot and make the new DCU completely disconnected from the old DCEU, it'd still make a ton of sense to make a third one if the second one grosses like the first one did.
That doesn't mean that Momoa Aquaman would be the DCU Aquaman, it'd just mean they'd make an Aquaman 3 not set in the new universe to close out that trilogy.
They have an easier time doing that too since unlike with let's say Batman it's much more feasible to just wait until 2030 or something to introduce the DCU Aquaman. The JL cartoon didn't even have him as part of the roster and it worked fine.
I'd actually say the same thing about Shazam. There is absolutely zero rush to introduce a DCU Shazam so they can probably afford to make a third one on the old DCEU.
And as for the "Well why cancel Wonder Woman 3 then?", it's simple: If you make a new DC Universe you need a Wonder Woman solo, you don't need Aquaman or Shazam. So they can plausibly keep going for one more film on their trilogies since it won't exactly cross paths with anything the DCU is doing, but Wonder Woman and Superman are characters the new DCU needs ASAP so waiting for them is not an option.
The answer is actually ridiculously simple. For some reason people have it in their minds it either HAS to be a hard reboot where Aquaman 3 and Shazam 3 don't happen no matter what even if they make a lot of money, or a soft reboot where those two characters will stay for another 10 years even if it causes a lot of problems for the worldbuilding of the new universe, when it literally can be as simple as: They hard reboot and they still make those films but separate from the new universe. The end. Literally zero reason they can't do that. It's probably the approach Gunn is gonna take for his Peacemaker and TSS spin-offs as well. They did well on HBO MAX and it's not like he needs to use Peacemaker or Ratcatcher 2 or Bloodsport any time soon in the new DCU so why not keep them going? There's genuinely zero conflict there.
Some people for some reason want this extremely clear-cut line between when the DCEU ends and when the DCU starts but due to the circumstances it makes way more financial sense to just phase out the succesful DCEU properties at the same time the new DCU kicks off with rebooted ones. It's like they demand that if it's a hard reboot then after 2023 nothing from the old DCEU gets made but that was never realistic. The transitional period into a full new DCU was never gonna be that clear cut with that amount of money on the line; but that doesn't mean the new DCU has to be compromised in the process by doing a soft reboot either.