It would a wasted opportunity if the guys never recorded anything in the studio together but I get how writing brand new music might be more work than any of them wanna put in on it.
So....how about an all covers album? Or...what if they take notes from the Page/Plant reunion from years ago and take old Queen songs but give them a new arrangement? Or what about taking old Queen demos and unfinished songs and just re-recording them with Adam on vocals?