While I confess I'm not aware of every detail of Rubio's life or background I'm not entirely sure why you would say that.
Unelectable? I'm not sure where this comes from. I googled his approval rating and the most recent favorable rating was 52/32 in Florida after the convention.
Corrupt? I confess I don't know what this is in reference to.
No record to run on? He's was a state senator for 10 years and has been a US Senator for two. By 2016 that would be 6 years. Obama was a state senator for 7 and US Senator for 3 years when elected. So if "no record to run on" is in reference to a lack of experience, there were many who thought the same about Obama (myself included).
Again, I'm not a Rubio biographer, but I like what I've seen. He's a strong fiscal conservative and is very good at arguing for its cause. In the few interviews I've seen with him (daily show and a few others) he has handled himself well and doesn't back away from questions. That is his biggest strength, IMO. As for him being Hispanic, obviously, that is something that the GOP could use (sad to think of it like that, but true). But I don't think talk of him as a rising star in the party is solely based on that. He's one of the few younger, more exciting people within the GOP. Obviously, all of this 2016 stuff is conjecture by all of us and who knows how the next 4 years will play out for the country as well as any of the candidates mentioned in this thread. But I certainly understand why many (myself included) consider him someone to watch.
He's been caught using party money more than once (if I recall correctly), he's been caught by the FEC for taking improper campaign donations, and he's had some, shall we say, very warm relationships with lobbyists. That's the kind of stuff that kills campaigns - especially when he doesn't have a record to run on.
Obama was the exception to the rule as far as not having much of a record. Every once in a while you'll get somebody who jumps ahead in the party and it's possible that the GOP's current state would make that possible for Rubio but I wouldn't hold my breath on it.
Additionally, his ethnicity will be no boon for his appeal to Latino voters. Outside of the large Cuban population in south Florida his race doesn't really do much for him. Most Latinos hate Cubans, and they certainly don't consider them to be the same race as them. Cubans are more closely aligned with whites than they are with any other Latino race. It's funny (in a very misguided way) that the GOP think they can just trot out a Latino name in an empty suit and immediately get back some of that 75% that they lost.
There's just not much of a benefit and a whole lot of downside.