Not been keeping up with the news lately? According to George and Bad Motherfucking Samuel, Mace Windu is alive and well.
I actually do think, if his performance in Hateful Eight is any indication, Jackson could pull off an old, jaded badass Mace Windu quite well. The problem with the character in the prequels was the material he was given and Lucas’s direction, it wasn’t his fault. That said, I think this would fit better in an anthology film (especially a Boba Fett anthology film, seeing as Mace killed his dad) than in the ST. In fact, I think that could work quite well. Set it between trilogies and it’s plausible Mace would still be alive (set it after the OT and he would be pretty damn old), and it would also help explain his absence from the OT. (If Boba kills him…)
In the ST, yes, I agree Coruscant is likely to appear and I wouldn’t have a problem with that at all either. Honestly, I didn’t have a problem with any of the locations in the prequels - Naboo, Kamino, it’s all good. The creative and visually striking environments were some of their few redeeming qualities.
As far as characters go… Well, uh, most everybody is either dead or was in the OT anyway so I don’t really know how to answer that.