Super 8 was proof enough to me that he's got the chops to take Spielberg on at his own game (and possibly even win
at it too!
I do think there's a dividing line between Star Wars and Star Trek though. I think if I'm being honest I'd say Star Trek's star had really faded considerably by 2008, so Abrams probably had a lot of autonomy on that production (a lot of people were genuinely surprised at how well it turned out), whereas Star Wars' had never really disppeared from the radar. People may not have liked
the prequel trilogy particularly, nor any of the fiddling-while-Rome-burns that Lucas did to the original films ("CGI Jabba"? Get outta here!), but I don't think Star Wars had the same kind of 'credibility problem' that Trek had prior to 2009. Lucas was able to relaunch SW any dozen number of ways and there would always be a cachet of interest in it... I'm not sure if Star Trek always had the same kind of goodwill behind it. So people were pleasantly surprised.
I think what I'm trying to say is that taking on Star Wars is a much higher pressure job than taking on Star Trek. There's more scope for failure in the Star Wars universe, especially if you're going to make a sequel that takes place after
the classic original trilogy. If Star Trek had bombed, IMO, it would have flown under the radar a lot more.
If Star Wars gets screwed -- even if it's not his fault, but rather because of decisions made by TPTB above his head -- then it'd be a career killer.