Answer
I wouldn't be surprised if we got only 2 or 3 new champions next year. In fact, I think we'll be lucky if there is 1. Some relaunches might be so expansive that they'll practically be a new release anyway. Even so, it wouldn't bother me one bit. It's better for the game anyway if Riot is serious about wanting League to stick around for a while.
Reasoning
<MAJOR BIAS ALERT>
The roster is pretty bloated as is. Anyone that says we need a new champion every 2 or even 3 months to stay interested is sorry to say, clueless. Look at the roster in it's current state and I dare you to say that champions are on average of about equal power but in their own unique ways. You can't and hope to be taken seriously. Balance (in-game and otherwise) has improved leaps and bounds since Season 1 but there are still major offenders.
I believe Riot's recent approach to balancing is good. I do not believe the pace at which they do so is. *note 1
I believe there are important people at Riot with the right vision in mind. *note 2
I do not believe Riot is doing all they can as far as support for other regions goes (event handling, competitive scene issues, allowing organizations like Garena to distribute their IP).
I do not believe Riot creating the League of Legends experience as well as they could be. *note 3
Note 1 - Riot right now are like a bunch of apprehensive puppies. They want to be happy and have you be happy with them but given the community behaviour/reaction in the past, they are afraid to trust or do what needs to be done. Lee Sin is a recent example I'll use. Should've and could've made changes awhile back, got scared off by the community despite:
- Vocal community knowing diddly squat about balancing with a track record of proving it over numerous years
- Knowing Lee is problematic as is
- Having big changes for fighters as a class that would've required Lee to be changed anyway
Riot should've bit the bullet back then. All this paranoia/fear of backlash is saddening. Some discussions will be heated and will take multiple tries but do what is right for the game even if it makes some people unhappy. Last I checked, Lee changes pissed off Lee players and Lee players aren't the whole community. The changes were good for the game and didn't take away the fun bits of playing Lee.
Note 2 - Ghostcrawler being against the idea of 'beginner' champs. Riot realizing the importance of fixing old code and champions.
Note 3 - Releasing a cinematic like a Twist of Fate and A New Dawn is cool and all but why not do that as part of reviving lore? We hear them talk about wanting players to know champions/world better but the cinematic goodness we get always depict battles on the Rift. Why wasn't a mini-cinematic done for the beginning/end of the Freljord event? We got good build-up with the Quinn journals, Lissandra login, Sejuani relaunch and the whole choose your faction thing. Then what? It just kind of stopped, disappeared. Spirit-guard Udyr comic introduced a skin, some Udyr/Ionia lore and acted as a promo for Ao Shin. And then... nuffin.
The cinematics we got were awesome but really, they were just fancy trailers for the game. We learn more about what champions are like from the Stick Figure spotlights. Look at how Waystone Games handles lore/events and take a page from their book. Surely Riot can match if not surpass it. What happened during the Rune Wars? Are Braum and Olaf descendants of the IceBorne? Hows that whole war in the North going? Who the fuck is the Ruined King and why is he spreading undeath? See all this stuff you have at your disposal for creating a League of Legends experience? Use it better.