These look like some good ideas. I've proposed similar ideas which I called "investor class" SP.

I'm not sure if 25% passive rewards would actually be enough, it may need to be a touch higher to compete with delegating to bots (even now) but it is probably in the ballpark.

The cold storage 'savings' idea is okay, but I believe there are plans for light wallets that don't have a whole account associated with it, and are free or at least very cheap and easy to create (doesn't require signing up with email, etc.). Since the sort of investment you describe is non-voting, it doesn't need an account and would probably be a good fit for those instead.