Thats certainly a new beta. You can see the other two beta's level selects here: http://www.s2beta.com/cheats Yours looks roughly halfway between the two in terms of completeness. Also, you really need to go to Dust Hill Zone and take some screenshots! Sky Fortress and SKy Chase would be nice too if possible. Really nice find!
Well, based on the clarity of those screenshots I would only assume that, yes - it's dumped. As to wether or not it's been released... well like Dot50 said, shouldn't you know? To my knowledge it's not.
It is not dumped. Edit: I know some source in Spain who apparently has this (or similar) version, so maybe it will be dumped soon.
If you have any other questions regarding Sonic or Megadrive protos, I'll be happy to answer them or help you in any way (by PM or something), I have quite a collection of them and I know my stuff.
It looks like a more advanced beta, anyway, I doubt theres going to be anything of Dust Hill there since several members of the STI group said that that level was never actually made in a playable form.
It is a later beta, possibly the most close to final beta ever publically released. About that Dust Hill thing - Dust Hill is called Mystic Cave in the final, the Desert level was NOT called Dust Hill.
Out of curiosity, since it IS running in a emulator, is there a chance this will be released anytime soon?
There are two betas out there already. This one looks to be unreleased though, from the screenshots. Where did you get it from Mr. Rare?