Ooh, cool question, yay. Well, in a universe where everything is possible and time doesn’t exist, my first choice would be Patrick McGoohan. I know all of you are going ‘bwuh’ but if you’ve heard of the 1960’s tv show called ‘The Prisoner’ he played the main character, number six.
He just has that perfect clipped BBC accent that can sound absolutely insufferable but still dapper, also RGB is ever so slightly influenced by number six, so there’s that.
If I had to pick someone from the modern realm, I have a feeling that Colin Firth would do a fantastic job. For one he’s got the right age to his voice, and has great vivacity, but he can also do that wonderful blustering stammer, which would be perfect for RGB’s pomposity.
Bonus: If it was translated into other languages I would love Hiroshi Kamiya to voice the Japanese dub. He does the voice for Trafalgar Law and Mephisto along with many others and is just one of my all time favourite VA’s.
someone asked me about VA’s for RGB again so here I dug this up