We don’t currently have a good way to delete a lot of users while still making sure all the proper hooks cleaning up data and sending signals to Discourse (and soon™ other Brainz sites).
I would propose a text box with one user per line. It should require at least two separate confirmations.
On the confirmation screens, I’m imagining a table (sortable?) with various editor information: username, e-mail, no. edits, no. votes, no. tags, no. ratings - maybe account creation and last login dates? Maybe IP hash list?
Nice-to-have bonus feature could be for it to send an automated e-mail to the mb-account-admin mailing list with information on the accounts that were deleted.