I think the league are in an awkward position where they have to strike a balance. They have to be seen as tough enough to pacify the other 19 teams, and the government (to avoid an independent football regulator) and like you say to not damage their brand by making it look like a league where the wealthy can just cheat, so what's the point in hoping for the best if you're not a supporter of that small group of clubs.
But what could also damage their brand considerably is 'undoing' too much from previous seasons. That messes with the belief people have in the certainty of its outcomes in the future, as well as drawing a LOT of attention to how long City were able to get away with it under their noses.
That's why I think stripping titles might be off the table, and any points deductions/fines will need to in that sweet spot where they're punitive but not so severe as to be a historic moment that's talked about for years and colours people's perceptions of previous seasons and the Premier League 'product' as a whole.
Something like a £50,000,000 fine and 25-point deduction would probably be about right (not right as in just, it's way too lenient - but 'right' from the perspective of these optics).