It`s not rocket-science; a lighter car, needs a less powerful engine and less heavy drivetrain, also fuel consumption is less.
A 4 banger is lighter on the nose and will improve steering quality ( although I like the 6 IL a lot)
So 1300 kg and 300 HP and a lot of Nm through turbo technology could be fine with me. But it is already clear that the 1 series have grown in size and weight compared to the outgoing E8X 1 series, so 1300 kg is a happy thought but can`t be real IMHO
There is another problem, how can this be done with already a M135i 6 IL and 320 horses? That doesn`t add up for me.
Most likely the 1M successor as 2M/M2 will be a down sized F8X M3 engine, more than 320 HP (M135i) and less than 450 HP (F8X M3 territory)
Anyway, let us be surprised