Delete/undelete rights are not a bid deal. There are persons at developed projects which take care about deleting and undeleting pages. The rule added for covering this issue may be very simple: using those rights at projects with regularly active administrators will be sanctioned by removing rights immediately. I think that it is fair enough and that every reasonable Wikimedian may agree with such rules.
How would you determine whether the wp in question has active admins? For instance, does tt.wp has active admins? I am not sure I would like to have my rights removed for rolling vandal edits back on one of the projects I did not see any admin edits for 30 days and then it turns out that I just did not notice smth. We are obviously not talking of large projects like en.wp or fr.wp., but of smth below 10K pages.
Cheers Yaroslav