Heh, I got beaten to the punch on that stage listing, but I'd point out that there are probably a few more with unlockable stages (DK64 and Pac Land aren't on that SSS at all). Also, I'm not sure why people think bigger is better on 8 player stages; small stages with large player counts emphasize skillful team play a lot more IMO since you have to actually play well specifically accounting for your teammates to accomplish stuff. I'd still never want to play on Temple, but Yoshi's Island (Melee) with 8 players sounds like the best thing ever especially at making sure teams of four players who are good at singles but are otherwise not a team will lose as often as possible to teams that are good at working together.
I'm unconvinced that walk-offs would be any kind of a problem at all on the scale of 4v4; I'm thinking your core stages would be the two BFs, Mario Galaxy, Eldin, Yoshi's Melee, Onett, Castle Siege, Windy Hill, and "any omega form" for 9 stage striking if unlockables don't give us more to work with in this mode. Temple, Palutena's Temple, and Great Cave Offensive are going to be poor stages no matter what, Gaur Plains is probably still pretty bad, and while 75m is near and dear to my heart, polarizing is the word that comes to mind.