In terms of concretely for this year (and not being a fiscal expert, just some rando on the web, as I'm sure you're aware) I see governments giving out help to people/companies in need, based on a comparison of current incomes/profits and last year's income in the same month. Not that that's perfect, but if it is workable, I don't see why this couldn't be generalized to the case where companies (or people, but that's probably a fringe) make significantly more profit now than last year around this time. Given the broad economic problems, that should separate out the winners of the crisis quite neatly. Paired with possibility for individual recourse, that should bring in some decent tax revenue and leave room for people who feel their increase in earnings is nothing to do with the pandemic. Of course, those people would have to make the effort to defend that case, and might also stand in the "court" of public opinion as a result.

Apart from that, I don't see why it seems a foregone conclusion that e.g. rent will have to be paid in full. That basically says "we guarantee that whatever happens, people who are well enough off to own more property than they inhabit themselves will not bear the consequences." I don't think as a hard-and-fast rule that's fair either. Because the inversion of that is "whatever happens, we'll have it be paid by those who have the least already."