It's interesting how everyone's experience is different.
Most of the people I've become buddies with in TM over the past 4+ years were either equally interested in United and TMNF or were United only players. Stadium was just one environment among many. I never went to LoL servers or the ilk.
If you're that scared that your buddies will all leave Valley and Canyon and only play Stadium, an environment you do not wish to play, then maybe you should get some new buddies.

I personally don't plan to play it any more than Canyon. And I'm actually a bit more stoked for Valley.
But having Stadium in TM2 will also be a new start for me with this environment. I plan to focus on building some tracks I can really be proud to release.
Also, considering that Stadium is what got me into TM in the first place, I refuse to speak ill of it. I wouldn't be here if it hadn't been for this lovely environment.
And I don't see how it feels strange to play Stadium after playing Canyon. The physics are completely different. I played TMNF about a week ago on a mini tech server and it felt quite normal.
I hope you can learn to be happy for the community in general and not begrudge people's happiness over something you may not yourself enjoy.
@wiidesire-2, Regarding the gamer.no info... yes I saw that... but I wouldn't call that official.

Some news sites are also saying that Stadium will be free, while people at Nadeo deny that a decision has been made about the pricing yet.
So you see why I'm a bit wary about news sites. They seem to assume too much lately. I'll wait until I hear it directly from Nadeo.