Re: How/When should the new Batman be introduced? In reboot, WF, or JL?
A solo movie would be preferable.
If they don't, and they have his first main appearance in JL, WF, or whatever, then I think I think they should have a little 5 minute scene in the movie prior to his main debut (probably in the credits), whether that movie is MOS2 or WW, clearrrrly establishing that it's a reboot.
(perhaps have a line regarding how long Bats has been around, show his reaction to Superman's arrival, the new alfred, the new mansion, etc) .
Surprise audiences and communicate it to them.
I think it might be a little dissapointing/confusing for GAs if the first glimpse they get of Bats is in the JL or WF trailer, and they're expecting Bale. Communicate it earlier in a previous movie, when audiences are already there in the seats.