Yoshi: Yes, but only cause I love Yoshis. Looking at it objectively though, it's not a good idea. Partners should be unique. We've already had a Yoshi partner before, and a main character like the Yoshi would be a bad idea. However, I'd love to see some type of side-quest that would allow you to play as Paper Yoshi! :D
I am always bored. That is a fact. Xbox 360 GamerTag - AceUltimatum101 || Smash Card - http://i30.tinypic.com/343rldx.jpg
Luigi would be too similar to Mario. Having Luigi as a partner would be like having 2 Mario's, except one wouldn't be able to wear badges and such. And even if they did manage to give him a totally unique moveset, still no. I like my classic Mario enemy partners.
As for Yoshi... Even though I love Yoshi, we've already had a Yoshi partner, and like I said, I like my classic Mario enemy partners. I can go to any of the other half a dozen games featuring Yoshi if I need a Yoshi fix, give me my unique Mario enemies as allies that you can't find anywhere else.