Do we have an estimated number of new champions coming out the rest of the year?

Well, if you count the one that was just teased.....I'd say max of 2.

But that's only if we get the new champ next patch cycle (7.16). 7.17 & 18 are going to be World's patches, so, expect them to be quite small in scope. I have my doubts about a new champ in 7.16, but I could definitely be wrong.

Then we have Evelynn, of whom I suspect we will see somewhere around 7.19 or 20, but only if the new champ comes in 7.16. If not, I suspect we'll see her with 7.21 or 22.

If the new champ is released on 7.16, I can almost guarantee that we'll have another champ for the year, which I suspect we will see come with preseason. If the new champ isn't released on 7.16, I doubt we will see a new champ until maybe 8.1 or 2, which I doubt we will some come in before Christmas.

the schedule atm is Freljordian Vanguard teased via horn -> mini-rework (new W is focus) -> VGU -> new champion -> VGU