I think they'd definitely do it. Google has decided to flip the switch and monetize as much as possible lately, having to use the Gmail app would be in line with that.
The benefit of gmail to Google is the intelligence gained for targeted marketing by scanning your email.
The worry that Google will disable IMAP misses this point. Google gains so much ancillary intelligence from scanning your email, that if they lose market share, their overall ability to target unrelated ads (e.g. during search).
