Well, actually, they have a God in mind. Dragon Ball Super is currently airing its Tournament of Power arc, but on Reddit, one fan threw out Hamill's name as a possible choice for the upcoming Dub version. Now, in his post, he says specifically that he isn't considering him for the God of Destruction Belmod, but once he made the connection other fans just couldn't see that casting go.
A few other suggestions were made, but the Belmod train couldn't be derailed. Fans admitted that it isn't necessarily the most original pick, but it doesn't really matter either.
"It would be cliche to have Mark Hamill as Belmod but oh so amazing. So amazing that whoever I hear as Belmod when the dub is released I will feel nothing but disappointment because this seed has been planted," ThatDamnBoyWonder said.
"BELMOD BELMODBELMOD man cant wait to see him talking in Joker s voice as BELMOD," Vivzkestrel said.
"I didn't even think about belmod being Mark Hamill, but now it's all I want lmao," SugaryCornFlakes said.
Kamken concurred, saying "I am ten billion percent okay with giving into that cliche."
The reason it would be cliche in some people's eyes is that Hamill is well known for his Joker vocal performance in any number of Batman projects, and is considered the defacto version in many's eyes. When you look at Belmod, you can obviously see where this suggestion comes from, as the powerful deity sports pale white skin, a large red nose, red lips, blue lines around his eyes, and two giant puffs of orange hair on either side of his head.
So yeah, you can't really blame anyone for drawing that connecting line.
Now, could this actually happen? Most likely no, though when it comes to castings you can really never say never. Crazier things have happened, but this casting will likely have to live on in fan's minds.