As much as many people seem to like Myles Kennedy, I firmly believe he's nowhere near as talented Scott Weiland was.
There are parts in 'Starlight' where Myles does an Axl-style shriek for seemingly no reason. I've heard he sings like that all the time. It's fine for that song, but him being in Velvet Revolver would probably make them sound too much like GN'R. It might be what some people wanted in the first place, but I was among those who were glad they decided to go with their own sound (neither GN'R or STP, but a fresh-sounding combo of the two) with Contraband. I wouldn't be looking forward to a Velvet Revolver record with Myles as the singer.
I have to admit I can't imagine anyone else fitting the band as well as Scott, and I suspect that's a big part of why it's taking so long, but I just don't think getting him back is an option at this point.