Yeah.. I think anything that tries to be retroactive is a non-starter unfortunately. Much as I would like it. Better to focus on punishing them now for all their past mis-deeds, whether it's money or fines. Do it in the context of this season. Hell you can take 50 points off them this season which will virtually guarantee relegation. And frankly if they are able to somehow survive it'll be entertaining as hell
I think you have to be retroactive to a certain extent - I mean if an athlete dopes wins gold, and fails a drug test, the guy who came second wins it. Essentially, we have financial doping in City's case.
However, the only period we can cover right now is the one the Premier League investigated - so we're just going upto 2018. In reality, City would never have had the success from 2018-the present without the earlier foundations - and I have a feeling that there may be more to come on the later era.
For now, I'd suggest:
40 point deduction - on this season - effective immediately. It still gives City players an incentive to try - in an effort to stay in the Premier League. Otherwise, their matches could be meaningless and this has a knock on effect for opponents.
3 Year Transfer Embargo.
Significant Financial Penalty - A lump sum to the Premier League to be reinvested into Grass Roots Football (not just given to clubs - ring fenced for grass roots - youth development, facilities, community football etc) - In the region of 300-500 million.
Secondary Compensation to clubs who have been affected by City's Cheating - factually based on prize money rather than projections.
All 3 Premier League titles from this period stripped. The 2011/2012 title awarded to United (Goal DIfference), the 2013/2014 title awarded to Liverpool (2 points behind). The 2017/2018 stripped but unassigned. They won the League by 19 pts.
If the fines aren't paid then the City ownership will be stripped of their "fit and proper" status as owners. Hugely damaging.
Additional Financial Controls and scrutiny to be placed on City for the next 3-5 years - an independent auditor will be appointed.