Other option
 

Why weren't Mick Taylor and/or Gary Moore considered, even back in 1975? Both were available, as was Ian Gillan.

I'd have been OK with these but...

After Dave Walker, I don't think they'd have considered Gillan, especially since that would've brought them back to a harder rock audience which they apparently wanted to get away from after dumping Walker.

Same "no hard rock" rules apply for Moore, especially at that time since Welch wanted to do more hard rock in '74 and they said no (and were horrified by the 1st Paris album) did they even know Moore? Even if Moore wasn't really "hard rock" then, what he was doing at the time (or soon would be) with Colosseum II (jazz fusion) would not have been agreeable to either party.

Taylor, for whatever reason, was burned out from the Stones so I'd be surprised if he wanted to jump right back into another "big" band (remember FM were considered has beens then insofar as what Brits, like Taylor, might have thought about FM then), especially since they wanted to get away from a blues based sound, so even if they got him, he may not have been happy musically (I know he joined that band with Jack Bruce after leaving the Stones, but if an offer from FM was on the table at the same time I don't think he'd have chosen that over what he ended up doing).

Not that I agree with any of this but this would be my guess as to how they might have felt based on what little we know about the way they seemed to want to operate. :)

John