I can well imagine Hannah is going to be rather displeased with Neville making that list, at a minimum it's going to greatly increase the number of witches interested in "poaching" on her interests; if Neville's really serious about her, he may have to take certain steps a bit earlier than he'd anticipated. OTOH, he's smarter and more powerful than given credit for, IMHO, and he may well be prepared, or quickly prepare, for that eventuality. That could get "colorful" in several ways.
It would be interesting, indeed, to see the reaction on Dumbles' face if Harry and Tom declared a truce and took care of him before squaring off against each other. I can't see Harry turning dark, not now, so an alliance is out of the question but a temporary truce to eliminate a "distraction" would be quite plausible.
Author's response
Oh Hannah isn't pleased with the list, but not for the reason you imagine. She understands Neville and knows that he wouldn't cheat on her...
I'm having some fun with the list.
As far as the final confrontation goes, no hints.