Agreed on your points. However there are some things that already in place. Ferrari already gets a cut of the top from TV revenues, before the distribution to the teams are done. I cant remember the exact figure but it is quite a heafty some. This can be increased to keep them in the sport as there is basically no F1 without Ferrari.
WRT the Williams situation, there can be a limit on the number of teams that can be supplied with a customer chassis, just like there is currently with engines. This will make sure that not everyone has the best chassis, and those who decide to build their own chassis will still be competitive against customer teams. BTW I personally think Williams has a very good engineering department with the current rules, and shouldnt have a problem being competitive against customer teams. They could possiibly be a provider of customer chassis based on their form this year.
For manufacturers to stick around in the sport, they need to have a tangible return on investment. The best return of course is to win, but since there can only be one winner, not everyone can achieve that. The other ways for a tangible return is to make the entry into the sport cheaper and to use relevant technology. Lower capacity and more efficient turbo engines are definitely the way to go - but the MGU-K and MGU-H isnt relevant, i.e. not used on road cars. Manufacturers want to use motor racing as a platform to demonstrate their technology and engineering skills, not spend millions on irrelevant technology.