Brace for impact, here comes a good amount of text.
I was never a big fan of King Diamond (especially his recordings) but recently he's been doing an even less pleasing job on vocals. Check the Roadrunner United track he sang on to see what I'm talking about, or his latest album. Granted, the guy isn't getting any younger but all the listeners (at least
should) care about is quality regardless of the performer's situation. For example, Django could only use three fingers of one of his hands to play the guitar, but that's definitely not why we care about his music.
Now Sneap is top tier, period; he knows his game more than well enough. He even managed to polish some real turds into records that made the bands rise and become big names (and I don't need to say names because every single one of you know what and who I'm talking about). Still, being on top of the food chain for a long time has its downsides and one of those is that you cannot afford to release anything other than pure genius in order to stay on top.
As producers, I'm sure neither of you would like to have your names on albums you're not entirely happy with for more than the overused "creative differences" excuse. It ultimately stains your curriculum because if the thing is not well received, both the band and the fans will try and find someone to blame for how much the album sucks. From personal experience, it's much easier for people to blame the mixer instead of noticing you haven't prepared properly for recording because, well, our current view of pop and music industry led us to believe "studio people" are supposed to do magic and hits out of literally anything.
That said, I believe King Diamond is not in condition to pull off a great album by
today's unrealistic standards. Would working with Sneap be an improvement from his previous works? Obviously; it's bloody Sneap after all. Still, I'm not sure about the current state of the source or the reception that would follow and because of that I don't think it's a great deal for any of the parts. Some things are better off left in the past as sweet memories and I can see why so many "band revivals" are done without recording new stuff, relying only on live shows.
This is just my personal, honest opinion; don't take it seriously if you don't want to. I'm not trying to start a discussion here, but I don't think this would work. With or without Sneap, for that matter.