That was what the 335is was supposed to be, but imo it feels so close to a 335 (bar the different transmission) that I'd choose either the 335 or m3 were I in the market.
Was the 335is a US market car? We didn't get it in the UK.
Since BMW already offer an F30 335i in MSport trim, the differences to turn it into an M335i would have to be worthwhile. And it would no doubt become more pricey, losing the M135's bargainous feel.