I think it's important for people to try and get inside Nintendo's head right now. If you were an exec for Nintendo and you wanted to sell DLC characters for a high profile game, what would your motives be?
1) Promote an upcoming game or franchise
2) Boost sales/awareness for the resurgence of an older/underselling title
3) Boost sales of the DLC itself by offering what the majority of the player base wants to buy
With 6 (techinically 5 now) slots of DLC left, which of these three would you choose? Answer: Something that preferrably knocks out at least two at a time. That said, here's my take (yes, just my own opinion) with regards to some of our most discussed potential DLC...
-Geno: Would count towards 2 and 3 with his inclusion undeniably counting towards long-standing fan service. He could potentially unviel SMRPG on the Switch Virtual Console or even a new remake/remaster of his original game to fulfill the marketing bonus of category 2.
-Waluigi: Would certainly count towards 3 but wouldn't really apply to 1 or 2 since he's never really had a game of his own (nor does he have one coming in the forseeable future). Granted, B-K had a couple of historic games under their belt, but given their status of being 3rd party with no games (future or past) to promote, fan service alone seems to be capable of swinging a character. ***Mind you, B-K was statistically PROVEN to be a highly demanded character via multiple high-sample polls. To my knowledge, the Wah has not seen a comparable presence until MAYBE recently.***
-ARMS: I strongly argue that this falls solely under category 2. Unless someone provides objective evidence to the contrary, it would appear that categories 1 and 2 are powerful enough to get a character added individually (hence Byleth, Corrin, Pokemon of the Week, the ARMS rep themselves, etc.). If ARMS 2 gets unveiled at E3, it will actually make even more sense since the ARMs rep will then meet both cats 1 AND 2.
-King Boo: Unfortunately, I honestly don't see him falling into any of the three categories. He wouldn't be promoting an upcoming game because it's already been released. He wouldn't be bolstering an older/weak franchise because LM3 is already a powerhouse. Finally, he wouldn't really count as "fan service" either since I'm pretty sure that he hasn't made a significant showing on ANY of the character polls I've seen nor has Nintendo put forth any kind of effort to increase awareness of him outside of being a semi-recurring boss in the Mario Franchise. This, coupled with the already over-saturated Mario roster in Smash really doesn't make him seem very likely to me. Then again, we got landed with Plant, so who the hell knows anyway?
LOL Wait, wait. So you cite a poll where Springman beat out both Geno AND Sora while the likes of Banana Dee/Shovel Knight beat out Banjo-Kazooie....and you think it's LEGIT?! ROFLMAO This poll is hilariously skewed. I'm curious what this sample group's demographic was. It's like going to UC Berkely and holding a popularity poll for Trump. If this thing held any real water, then why hasn't Banana Dee, Crash, Decidueye, Shantae or Isaac been added as fighters yet? Also note that ARMS was still relatively fresh in 2018 and we didn't see the first round of newcomers for Ultimate until August 2018. Amazing to see how expectations change over time.