So I must be in the minority but I thought SGU was a good attempt of a soft reboot of sorts (stranding them across the universe and changing the tone of the show). New rules but still exists with the current established universe.
I think a full reboot is in order. Like BSG. Take some of the basic elements that makes Stargate Stargate and build something new. Change the rules a bit (I liked the fact that Stargates in Universe weren't powerful enough to gate anywhere in the galaxy, that to get to one side to another they had to gate to several gates along the way). New characters and reimagined (or better yet, original) aliens. Just start a new but with similar concept (modern day humans traveling across the universe). I don't think any other option will work really. Stargate isn't popular enough for a feature film. So a mini series to reboot it, that can happen.
Sadly unless someone buys the Stargate franchise off MGM I don't think any of this is gonna happen. They only made Skyfall with help and they are whoring the crap out of Bond (beer commercials. Really?) to make extra cash on it.