With the WiiU Pad (possibly 2) being used there is no way that smash (with 2 WiiU Pads, the maximum frames per second are 60; all 3 smash games thus far run at 60 frames per second), with items on very high that 8 players could play without lots of noticeable lag, even offline, given how detailed the character models, items, item-related characters, NPCs, and stages are/will be, even with 8th generation of gaming hardware. Maybe without items it would work, but smash's super content would hold it back in this case. All the Pokéball Pokémon, Assist Trophy characters, and Final Smash/Super moves would be total overkill. Could y
That doesn't even take into account that Smash WiiU will probably only have 4-6 controller ports. Oh, and I doubt Smash 3DS could handle it either, especially with its' weaker processing power (because it is a handheld console of course).
Really, 8 seems like a huge jump, especially with like 8 Ice Climbers (16 characters), items exploding everywhere, loads of Pokéball Pokémon, Assist Trophy characters, and Final Smashes. Really, 6 seems like it would be the "cap" for now, and even that is stretching it (especially online, even with Namco Bandai making some good online systems in the past). Heck, I don't even think the 3DS can handle 6 players like that, and with the WiiU, I'm not sure if it could handle it with a WiiU Pad (or 2).