I wouldn't mind a return to the somewhat more serious Saint's Row 2.
You can never have too many games like GTA. Its not as if the market is flooding with them.
Apart from Saint's Row there's only Sleeping Dogs.
There are more Zelda, Baldur's Gate and Might & Magic "clones" than there are GTA clones, yet that does not seem to bother anyone.
I'm not sure where they can go with the series though, perhaps a reboot is the most likely way ?
And 'yes' I want a new city, its never fun when games re-use the city from a previous game.
I would not mind a revamped modern visuals Stillwater in the future. While Steelport looked much better at first glance SW felt more alive and diverse than SP. At least SR3 Steelport. Did it get pimped in SR4? Heard SR2 Stillwater was also much better than the SR1 one.