As a question, how many retro characters have been supported to join Smash before appearing as a AT or stage character?(people like Game & Watch and Duck Hunt and not like Littie Mac)
Good question. Most of Smash speculation started around Brawl, as it would be the sequal to Melee, which was the definetive Smash game to hook people onto the series. We had at the time Ice Climbers which was unique for being a dual character, which was new. And no one really knew Mr. Game & Watch, very few people knew who the character where supose to resemble when they first encountered the "New Challenger" sign of him back in Melee.
Brawl was more on those characters we did not have. Diddy Kong, ANY Kirby character, Ridley, Krystal from Star Fox, Geno from Super Mario RPG, and Sonic where huge names back in that game. Therefore, no Retro where that much thought upon. We did not know what WTF characters where back then. When there came a leak with R.O.B on it, people discredited it right away, and when it was known that R.O.B actually were part of the game, people really got salty, and really hated the inclusion. So, a negative O for Retro's during Brawl.
Then we come to the recent Smash 4, which was going to feature 3DS and Wii U version. Now, with most notorious fighters present in Brawl, with the likes of 2 new Kirby additions, Olimar for Pikmin, Wolf for Star Fox, and Pokémon Trainer, people rested easy, and sprung up their diet coke can of character possibility, and everything popped out.
When we got Mega Man, and Wii Fit Trainer confirmed, it really branched out. We got yet another Game & Watch, and R.O.B character in Wii Fit Trainer. We got sad, really sad to know that our beloved Ice Climbers would not return, and knowing that cut's came around, people where afraid of losing others, and as time went on Charizard was a stand alone, people lost their mind. Ridley, yet again, dead. WHAT IS THIS GAME EVEN, we thought.
Still, in the wake of this time period, we had a small group for Lip. A big one for Takamaru, as Pit's Brawl debut made it apparent that, Pit, Samus, Link and this time their last same year guy, Takamaru would debut. Even Mike Jones had some support at that time. As with Lip, a very small fanbase for Balloon Fighter were also present, perhaps the two underdogs of the Retro this time. The biggest underdog, was Duck Hunt Dog himself. One guy was out of his mind crazy obsessed with getting that laughing dog into Smash, and HE was the one who got his wish through.
Now, for Ultimate, I'd say, now that Taku is gone, and people feel like Villager's up-b would disconfirm Balloon Fighter, people have started looking into two Retro picks. The most notorious one is Excitebike Racer. I personally don't see him feasable, nor interesting, and the other one is Lip, perhaps in the minority, but visable.
Retro is actually something we have come to expect, this time around, and was more something we got really surprised by earlier. Now that we start to see "patterns", which is not even there, and trying to unlock the mind of a madman/genious, which NO ONE will manage to predict, it's just to give up, or have fun with the speculation.
Regarding Little Mac. Since his inclusion in Brawl as an Assist Trophy, he got notriously big on the request scene, but because of the Wii Game for "Punch-Out" people did not view Little Mac as a true retro. Hence why I never mentioned him in the analyse, but I guess I should clear that out since you mentioned him specifically.
That's my view of the Retro battle in Smash.