If banned members tries to log in, will the login attempt be visible as their last visit - or does this date only mean the last time they actually were logged in?
I just tested it. Banned users do not create a xf_session_activity record for their actions, including logins. So their last activity date does not change after they are banned.
I think it's very interesting information. "The user was last seen 'trying to log in'" is still valid, imo. They were still here, although not fully logged in. vBulletin works like this, and I miss it.