I think I have waited long enough.

Spoke to a BMW product genius in Aust yesterday regarding if the B58 will be replacing N55, the answer is no, B58 will be use on 3 series or higher...

Don't know how accurate it is, product genius sounds just like a salesman in disguise that know bit more about the tech stuff.

Well, i am in the process of sorting out the $$ stuff before commit to the m135i regardless if it is B58 or N55. The main concern is the arc spray liner will be as durable as the iron liner. The porous surface is good to retain lubricant, and also dirt/debris too. Well, time will tell. Unless you plan to keep the car for short term, this will not be a concern.