My 2 cents on this.
I owned and liked the 35 Art very much. I then decided to get the 50. Wow, that's even better. When the 24 came I wanted that for starscapes and stuff. So I got the 24 but couldn't really justify having 24, 35 and 50, mainly because of 24 and 35 being so close to each other.
So I sold the 35. And I miss it.
Still, the combination 24/50 makes more sense in my camera bag, but I want the 35 back, somehow. As I can't use the 24 at f/1.4 anyway for starscapes because of coma in the corners, this 24-35/2 somehow comes in as the perfect compromise now. I lose f/1.4 but I (probably) save money compared to having 24 and 35 primes and I don't have to justify owning both primes.
I for one find this lens very interesting and will definitely give it a go when it comes and probably even consider buying it itf it's not too far away from the MSRP of 24 and 35. Of course if it's way over 1000€ I can get 24 and 35 used for almost the same price so that wouldn't make sense but let it be say 999€ MSRP which is more like 849€ street price, count me in.