My first Mario game was New Super Mario Brothers Wii, and I remember playing it for the first time and thinking, "man, I'd love it if I could just ride on Yoshi for the entire game". Imagine how I felt when the 3DS ambassador program introduced me to Yoshi's Island for free several years later. Now that I'm actually good at platforming I'm more interested in difficult games like DKC, but I'll definitely be keeping an eye on Yoshi's Crafted world to see if it's worth picking up anyway. Anyway, point is I wouldn't mind more Yoshi content, especially if it comes from Woolly World or the original Yoshi's Island.
As to whether I consider it its own series or not, I ask why does it even matter that much? As long as a new Yoshi character brings more variety to the roster, I don't see why it's an issue if they'd be "over-repping" the Mario series or not. We fans tend to hold "representation" as the holy standard for which all characters should be considered or scrapped when there's far more to each character's inclusion then just that. While I'm not a huge Kamek supporter, I do think he has to potential to make an interesting fighter with a little creativity and think that people who like him should feel free to support him or any other Yoshi character they might want regardless of how "well-repped" Mario is.
Although if you must know my opinion, I consider Yoshi both a Mario rep and a Yoshi rep. He clearly represents his own series through his moveset and unique symbol (obviously), but he's still Mario's iconic partner. I don't see why it has to be just one or the other. I feel the same way about DK to a lesser extent, since he's still Mario's iconic rival and has been associated with the plumber long before he became his own thing. Heck, maybe we'll even see K.Rool in the next Mario Kart (although if we couldn't even get Diddy in MK8 I wouldn't get too excited about it).