I did some tallying, and determined that out of the 75 icons on the character select screen in Ultimate after everyone is unlocked and Piranha Plant is downloaded (counting Pokemon Trainer as one character), 39 (more than half, which precisely is 52%) go to characters from the Mario series and its spinoffs (14 characters, 3 of which are new), Pokemon (8 characters, again counting the Trainer as one, with Incineroar added), Fire Emblem (7 characters, one being new), The Legend of Zelda (6 characters, all veterans), and Metroid (4 characters, 2 of them new).
Another four franchises have been determined to have three characters each - Kid Icarus, Kirby, Mii/Super Smash Bros., and Star Fox. None of the four currently have any new representation.
Still another four franchises - Animal Crossing. Castlevania. EarthBound. and Street Fighter - have two characters. The former and latter have one new representative, Castlevania is a new franchise to Smash.
The remaining 16 franchises - Bayonetta, Duck Hunt, Final Fantasy, F-Zero, Game and Watch, Ice Climber, Mega Man, Metal Gear, Pac-Man, Pikmin, Punch-Out!!, R.O.B., Sonic, Splatoon, Wii Fit, Xenoblade Chronicles - each have one character. Of these 16, only Splatoon, with Inkling, is new to Smash.