So when is the new champion coming out?

If I recall correctly, I saw a Rioter mention that they were not planning on releasing the newest champion for a little while; they wanted to focus on the new skins (the Project Skins). However, if you remember, the same Rioter who created Braum, the sassmaster support, also is creating this new champion, so it will probably be reallyyyyyy awesome.

A new champion or a teaser for one will come out after patch 5.18

tomrrow

I'd say either in September or even in early October. They can't keep putting Legendary skins on here and it doesn't sound like most of the re:work champions are finished yet. Its been June (Gangplank, Miss Fortune, and Fiora's updates) and now August (the Juggernaut update). They can't go the whole LCS and think they shouldn't release a champ. If anything, sometime either this week, or next week we might get a teaser. (I know some time in September we should.) And then after a week, he/she will be on the PBE for 2 whole weeks of testing. Hopefully, this Rioter will ask for anything wrong and listen to our opinions. So, by mid September to the end we will see something. I'm hopeful for Ao Shin since it was said we wouldn't see him all last year and he may be ready by this years end. Other than that, there's a new ADC in the works they can release (a Darken supposedly ready or almost there) or maybe something completely different.