Yeah, I quite like your idea of SAT. My only concern is that it introduces one more level of complexity to a system which is already quite complex. But maybe in this case it's worth it, especially if it makes the referral system easier.
Yet maybe for now the easiest way out is to just allow users to raise SP via posting and then use it to create new accounts for their friends. Or just spend their own SP for that purpose. I would gladly do that but I cannot - unless I am not aware of this functionality in Steem (please let me know if that's the case).
If we remove SBD at the same time, the overall complexity doesn't get higher. It might get even a little bit smaller. For SAT, there is no need for price feed because the price of one SAT is set by witnesses, it's the account creation fee.
It is possible already. Any account can create as much new accounts as they want (if they just have enough steem to pay account creation fee, which is transferred to the initial SP stake of the new account). But Steemit.com hasn't yet implemented it in the UI, you have to use cli_wallet instead.
There are a few problems in this, even if it was easier.
Psychologically it might be better if users have tokens that can only used for account creation and for nothing else. Although it can be transferred (which enables it to be used like a currency), its primary function is account creation so that's how most people will use it most of the time. And it's much easier for the community to watch if the rewards of posts are used for helping new users or not.
Then there might be regulatory benefits. Of course the taxman does what he pleases, but it might be possible (at least in some jurisdictions) to make a claim that SAT is not taxable income – the purpose of the token is to help the system get new users, not to make money for the person who earned it. Basically it's just a right to decide who can get a new account on the platform, and not income.
For me SBD is a fundamental part of the ecosystem. But I get your point: SBD is quite useless without the peg.
That's really a shame. In HF20 they aim for a mobile app, yet still the basic functionality is missing on the webpage. A classic example of messing up the priorities.
"Psychologically it might be better if users have tokens that can only used for account creation and for nothing else. Although it can be transferred (which enables it to be used like a currency), its primary function is account creation so that's how most people will use it most of the time."
While I do support the sponsorship model for new account creation, the statement I quote here is an unwarranted assumption. For example, people can buy stuff with Air Miles, which were never intended to be a currency with that potential for use outside of airline promotions.
Without deliberate breaking of functionality of any token which is tradable, it is impossible to state categorically that it won't become just another currency.