I'd like to see emails bulk-imported validated during the import. For this particular project most of our list comes from clients that walk in the front door. Their emails are added manually to our billing database, then exported from that, then imported to the e-newsletter plugin.
We occasionally have typos that include an extra space, dot or other 'illegal' character. All things that don't pop visually in a long list. Thus, when we send, we'll get an error message. The only way to fix it, to continue the send seems to be to go into the database itself and fix the offending email (or delete it), then continue. (Not a problem for me, but I wouldn't trust the client in the DB!)
Anyway, since the validation function is already part of the system, it would be ideal if it would run on each address during a bulk import.