Thank you for taking time to put this on writing! Excited about the future.

Vote expiration for witnesses, proxies, and proposals

This mean if user sets the proxy, they have to renew as well right?! Because if proxy performs governance action, proxied account also getting last action updated means everyone would potentially proxy. Once a year is quite reasonable, especially notifications and email subscriptions could be handled by frontend.

HMT

Would great to explore/research idea of creating token on 1st layer and customizing it on 2nd layer solutions. Like define initial token parameters and assign account to perform future changes only to certain areas, of course supply and other critical parts shouldn't be allowed to change, but with proper migration technique it is possible to create robust system. If token needs critical changes there could be migrating mechanism to define new token id and old token would convert to new token with different parameters, just thinking out load but this could be researched deeper.