I’ve said it before but as long as Steve Harris is at the helm, it doesn’t really matter who the producer is. I imagine a more hands on producer like Sneap or Roy Z would fight Steve’s wishes until finding themselves out of a job. Then you have an album produced by Steve without any other input.
Shirley is the best guy for the job. He knows the band as musical personalities and is able to make really good sounding albums with minimal processing (see Counterparts by Rush). If Steve would stay out of his way, we’d have more albums like Brave New World, which is one of the best sounding modern metal albums.
And have Maiden sound like every other metal band, as @srfc indicated? I agree that DOD and TFF didn't sound great; I found an explanation for DOD a long time ago (it was supposed to be a 5.1 album, he didn't realise that's not the way of the future) and TFF, although not great, wasn't horrible either. BNW and AMOLAD have a unique and amazing sound, and there's nothing wrong at all with TBOS.
Firepower is a good model of what this would sound like. A classic 80s level of pristine but with modern technology and sound. I’m skeptical that it would fit the proggier sound of modern Maiden. For what Priest are currently doing it was perfect (if not somewhat generic).