The only way in which a different Batman from Pattinson would make sense, is if tonally it's a completely different take. Like, full on kid-friendly, outlandish, Justice League Batman (done well).
I won't give a damn about it, because that's not the Batman that interests me, but I could see the value in it for the broader, younger audience.
If Gunn is going to do that, while retaining Pattinson as the 'black label' Batman for adults, that'd be a decent strategy.
In fact, I'd go so far as to have two strategies laid out: one for the PG DCU, and one for the R Rated Black Label DCU. Let Reeves get as dark as he wants, while keeping the more lucrative version for the younger audience.