I'm personally of several opinions as to this question...
My very 1st reaction during the Grammy performance was, "hey, Rush has been doing this on tour now for years (flying in triggered backup vocals and keyboard parts etc...) and it never bothered me much... (well I guess it sorta did at first....)
As for the Andy and Stewart route, could certainly work on some of the older songs, and part of me certainly perfers that for this tour (just the three of them on stage, raw etc... like Sting said, sounds like a very nice proposition)...
There is another part of me (please don't laugh) who, definitely rather than the MIDI sequenced stuff from the Synchronicity tour, would not have minded at all, say, Kipper or J. Rebello on keyboards and Dominic Miller on additional guitar, as this suddenly opens up quite a few of the Synchronicity and Ghost In The Machine songs. Additional keys and guitar on stage, yes, but live...
Perhaps three MALE backing vocalists might have worked... certainly won't be missing Tessa, Dolette and Michelle (nothing personal against them...)
Now, if it is going to be just Sting/Andy/Stewart on stage, I suppose they could still play just about anything. Expect quite a few new rearrangements, though (new 2nd verse of Roxanne, the "Voices Inside My Head/When The World Is Running Down" new midtempo funky version from the Whisky, which by the way I just can't get out of my head... love that bassline, harmonics on the guitar, and midtempo groove, perhaps as close to new music from The Police as we'll get for a while??)
I, for one, won't mind either way...
Laz