I'm alright with Bowser being the main villain in most games, but I do like the occasional game with a different villain. Before changes to the main villain, I'd rather there be more variety in the sub-bosses. For example, I would have liked a little more variety in the Super Mario 3D land bosses.
Generally, though, I'm okay with what's been done as far as main villains go. I voted other, though, since I don't have a strong opinion either way. More varied villains could be pretty interesting.
Make a Mario game with all the villains team up (not the ones who became good guys at the games end) and have all of Mario and his partners from the past games (Paper Mario, Super Mario rpg, M&L series, etc.) team up somehow and battle in a big war. Boy, I don't sound like myself right now. Think it's the food I ate.
No. I believe that Bowser( or other villains like in the Paper Mario series) should be the main villian in the other video games coming out in the future.