There were two men dancing together on DWTS Ireland and on Dancing on Ice. It's not a first, though it's probably a first on the BBC!
In my opinion they should be good dancers first and a same sex couple second if they are to win. I don't care who dances with who, but I do think that same sex couples are often more boring to watch, you might as well be watching on person dancing on their own in front of a mirror a lot of the time. For me, the interesting thing about Strictly is watching the couples interact, and part of that is watching the different size/shape/strength of bodies working together to make a beautiful movement.
With John and Johannes there is too much dancing side by side, too much mirroring, too little interaction (in my opinion) to make it as interesting. They were great early on, but as the other couples have progressed I think they have stayed much the same as they were at the start.
I would also prefer to vote for the winners on dance ability rather than simply the fact that they are achieving anything, or breaking down barriers or anything else.