I think guest accounts should be as limited as possible. I really like what SteemPeak already has in place.

So anything SteemPeak stores about the user off-chain could be available to a guest account. And anything that needs to be broadcasted to the blockchain is unavailable to guest accounts.

The thing I really want is the ability for guest accounts to enable full blockchain accounts without having to capture the keys. If they want to, great. If not, they should be able to continue to log in with their other social accounts and let the front-end manage the keys.

In fact, I think anyone who wants this "key management feature" should be able to associate their social accounts with a trusted front-end. This might mean they want someone like SteemPeak to fully manage their keys, even though their blockchain account originated elsewhere.