As far as I know, there is no exchange using coinhive miner. And pretty much adblocks can block it.
So, why Cobinhood there is no fee...
Are you talking about
https://cobinhood.com/ ICO?
I'd say that they're probably making that much money off their ICO, that there's no need for any fees in the near future.
Also, i believe they have told themselves that they will "underwrite" ICO's in order for them to generate revenue in the future.
I actually asked their "customer service" what the tokens do. This was the response....
"If you're a COBINHOOD ICO participant, then you will receive COB tokens which give you exclusive VIP privileges in COBINHOOD. When COBINHOOD underwrite ICOs, COB token holders will have the privilege to get future ICO tokens at lower rates than normal ICO participants.And the best part is, the actual rate may be as low as ZERO!" -Ken
I responded- "to clarify, all I get is a discount on future alt coins?"
Ken-"yes."
https://www.reddit.com/r/Iota/comments/712h9d/theres_a_new_ico_that_claims_it_will_be_a_0_fee/dn8amj1/