While I agree that it would be useful (though extremely difficult) for administrators to manually specify the automatic reversion of all changes by a user (as suggested in Bug 520413), I don't think that all changes by all users suspended for abuse should be automatically reverted.

Besides the problem that you allude to (that an account could be wrongly disabled and later re-enabled), I see four problems with automatically reverting all changes by suspended users:

(1) Some users might contribute significantly, and then their login credentials could be obtained by a spammer or otherwise abusive user. If you contributed to numerous projects in numerous ways over a period of years (or even if you contributed just once to one project), and then you logged in on a computer infected with malware and got your Launchpad identity stolen and abusively used by a third party, I doubt you'd want all your contributions to disappear overnight. The other contributors, and end users, who benefited from your contributions would probably be pretty unhappy about that too.

(2) There is another plausible, though much more unlikely, case, in which a user who contributes significantly becomes abusive. That could certainly justify suspending their account and reverting many of the changes they made on Launchpad (the abusive ones), but it would not justify reverting the others (the non-abusive ones that actually contribute).

(3) Such a feature, and (to a slightly lesser extent) the feature requested in Bug 520413, would arguably have politically bad consequences within the community. Erasing the impact of a user is currently difficult and has to be done through positive actions of other users (who can be credited, and thus also blamed, for doing so). That makes it less likely that personal attacks will escalate into the inappropriate labeling of an unpopular user as being sufficiently abusive to warrant suspending; it also makes it less likely that angry users will delete other users' edits to get back at them. I am not suggesting that such behavior is a major risk on Launchpad, but it is a real risk, and I think that the potential benefit of better protecting our community from abusive users should be weighted against the possible harm of giving people powerful ammunition with which to make bad situations worse.

(4) Automatically reverting all changes by users suspended for abuse would actually constitute a security vulnerability. Besides the obvious exploit of targeting committers of security fixes on code.launchpad.net for identity theft and spamming with their identity to get their security fixes automatically reverted, there's an additional, more subtle possible attack: A user could create a Launchpad account, fix one or more security vulnerabilities in one or more Launchpad-hosted projects, and then, after a substantial duration, act abusively until his/her account is suspended. Then the security vulnerabilities, long ago believed (correctly) to have been fixed, would come alive again, and he/she would know about their exploitability long before anyone else would likely figure it out.

(Of course, that illustrates one of the problems with the claim in Bug 520413 that all changes by a user should be automatically revertible--on Launchpad, users create content which is then modified by other users, so the impact of a user cannot, in general, be rolled back.)

On the topic of not showing comments by suspended users--if users still have some way to view the comments if they wish to, I think that's probably a good idea. For example, the comments could be retained in the full activity log, and there could be a note like "M comments are not shown, because they were posted by N suspended users. To see them, see the full activity log."

Another possibility would be, for pages where there are comments by suspended users that have not been manually deleted, to have the following in lieu of the "See full activity log" hyperlink:

"See full activity log (contains M comments by N suspended users)"
"See full activity log without comments by suspended users"

If we do something like that, then it might be worth noting somewhere that comments by suspended users are subject to deletion; we wouldn't want to give people the impression of a policy that anything ever posted on Launchpad, including spam, is retained.