I think he is more cute and kid-friendly than cool. Sonic was cool. He was a badass punk SOB.

Mario can be cool:

https://www.youtube.com/playlist?list=PL6BmNUG1JZAqnQcA3aN-eYxOF6-_9eTrl

Mario is always cool. He's retro cool, he's gamer geek cool. People love him and the game in MK8. People loved his return in NSMB, and SMG was definitely cool. NSMBWii was massive. People are down on Nintendo right now because their systems aren't selling as well as last gen, but people still love Mario. They OD'd us a bit at the start of the Wii U life without giving us variety in other titles and without big innovation in NSMBU and SMB3DW. But MK8 nailed it and a new platformer adventure title could easily do that as well.

mario used to be a bit more hardcore in the old days thats what made him cool..now he is more casual but every once in a while we see games like Galaxy and he makes a comeback as the coolest in the industry.

I'm gonna have to disagree with you on NSMB selling due to casuals. 2D mario always sells more. And is pretty cool.

Based on the OP it sounds more like you want him to be completely new and fresh again, which is impossible now.

It is not Mario that has changed, its us

Galaxy was cool. And gave me a SMB 3 feel. So it's possible, it is just waiting the right moment. Because you know, "he is there hero we deserve, but not the one we need right now".

Mario will never again be cool. He might be fun, but he will never be cool.

Only if Mario is wielding a gun in first person. That's the new cool. Do I agree with it, hell no. That's why Sora's getting guns, he needs to keep his cool from the PS2 era.