Sold pretty well. Ranked Pokemon Stadium 1 as the #6 best-selling N64 game (counting N64 bundle purchases) and Pokemon Stadium 2 as #18.
Personally considers Pokemon Colosseum and Battle Revolution as games in the same vein. (Disclaimer: Never played them.) Allowed you to transfer your Pokemon from the main games to these games. Focused hard on just battles, just like the Stadium games. Ported the models from Stadium 1 and 2 into Colosseum too. Misses out on (some) rentals and minigames, sure. Traded rentals and minigames for an expanded story mode, for better or for worse.
Reports decent sales numbers for Colosseum. Ranked #9 among all Gamecube titles at 2.41 million sold, just a hair under Pokemon Stadium 2's numbers. Went less well for Battle Revolution. Made it to #41 overall, with 1.95 million sold. Was in a much bigger market, though. Compares unfavorably versus Super Smash Brothers Brawl at #8 with 13.32 million sold.
Doubts much chance for a new Pokemon Stadium. Asks the inevitable question: why was this not in the mainline game? Sold Pokemon Stadium by putting 2D Gameboy sprites into colorful, 3D models on your television. Already appears on your television whenever you want. How are you going to convince Pokemon players to fork over $60 for the main game, $30 for DLC, and (probably) another $60 for slightly fancier battles? Copies over the models from the main game for sure.
Sees only one way forward for a new Pokemon Stadium: battles like the anime. Must look wildly different from the main game, in both models and animation. Imagine a battle with Pikachu versus Machamp. Physically punches Pikachu in the face, not just hovering a fist icon over Pikachu. Freezes the animation with Pikachu in mid-air as you pick its next move.
Would people buy it? Shrugs. Depends if it has a story mode, probably.
(Re: the title. Belongs here in Pokemon Gaming Central, as a spin-off.)