Smash Run
There were those leaked screenshots which we don't know for sure was legit or not (
link). Some aspects don't match what we see today, but it did look like higher resolution Smash Run and so at least some work went into it making it not look like a 3DS screenshot if it's not legit. We know that SSBU wasn't built from the ground up, and is instead built on a base from SSB4, and since it was a while ago, those discrepancies could be ported Smash 4 assets that were being used as placeholders and have since been replaced (the character icons and such, for example).
So there is still a pretty good chance those leaked screenshots were legit. A build from spring 2017 or earlier could very well look a bit different from the E3 2018 build. That said, there is also definitely a chance someone went through the effort of making higher-definition shots of Smash Run locations, the Paper Mario stage and Yoshi's Break the Targets stage from Melee. If so, they did a pretty good job, though. Would've been time consuming.
Smash Run chances: 50%
I guess it was pretty popular, and it might be a popular online mode if they keep it for SSBU. I'm not convinced that leak is legit, so while it improves the chances, it's not a guarantee by any means.
Smash Run want: 50%
It was alright. On the one hand, it's more fun than some other modes. Definitely better than Smash Tour, the Angry Birds mode or Coin Launcher.
On the other hand, if you have to do it with every character to unlock stuff, it's going to be more than a bit of a grind to have to do it 68+ times. For a completionist like myself, the time commitment for the single player modes has to take that into account. Smash Run takes 5 min for the main portion, 1 min for the final battle, and some additional menu/loading/results time, etc. so about 7 minutes per character. That's a lot longer than other modes per
try. Smash Run isn't fun enough for me to want to have to spend a minimum of over 8 hours on (~7 min x 68+ characters), assuming I complete it satisfactorily on the first try with every character. I prefer less grinding tasks for unlocks.
On the third hand, this is more of an issue with how they design rewards than Smash Run per se. Hopefully Sakurai has realized that having rewards for "doing X with every character" should try to avoid being too difficult or time consuming. That is "play Smash Run with every character" is better than "finish first in Smash Run with every character", but since Smash Run is already relatively time consuming, even
that is going to take a long while (8+ hours! Although at least on Switch you could potentially cut the time by 3/4 by having four human players?).
As a tangent, I find Break the Targets to be a pretty fun mode, since it has more puzzle-like aspects and basically no luck-based aspects. If that leak was legit, I'll be happy to get that mode back (with character-specific layouts again!). I'd also be cool with Board the Platforms and Race to the Finish coming back.
Nominations: Break the Targets returns x5