I'm not super-familiar with LoL either (its older sibling / rival Dota 2 is my forte - having played that a lot between 2012 and 2017, and I still watch that), but I do have some familiarity with it thanks to having watched a lot of LoL and having delved into some of its characters. Ahri's been at the center stage ever since she made her first appearance in (I believe) Season 2-ish (if not early Season 1) - partly because she's considered one of the most dynamic and exciting characters to play (the other reasons... well, yeah
). Some other champions of note include Ryze (one of the centerpieces of the initial reveal), Renekton (one of the most popular tanks, partly because he's a ****ing croc), Jynx (very popular Harley Quinn esque character and centerpiece of LoL's marketing), Draven (LoL's resident "If Heihachi was even more of an egomaniac meme" character) and of course
.
LoL has a pretty decent shot, but it would be quite tight timing for Riot / Tencent because Tencent only started to collab with Nintendo seriously around the 2017 / 2018 window. It depends IMHO on a number of factors - if Smash Bros is indeed one topic that Nintendo and Tencent / Riot discussed or even partnered over when they entered talks being the primary factor. Now I would not be surprised if Smash was brought up in the talks - and not just because Riot is one of many, many studios that would gladly take the opportunity, but also since Tencent's MO is heavily based around multi-pronged projects, collabs and promotions (Pokemon Unite is certainly a part of this, as is the Switch's release in China - which Tencent handles).
I honestly find it difficult to call whether or not such talks lead anywhere in regards to Smash, and it's a main reason I can't say LoL's a frontrunner. Still, I definetely count it as a dark horse - especially for E3.
Of course, I'm reminding
3BitSaurus
because he's the guy that's most familiar with it (2 support threads after all).