I´m still not completly sure, as EnI and Scott have always said that is will be created by the M Division but wouldn´t have the M badge.
Problem:
M1 trademark has a certain cache. Marketing guys know it would not be wise to put such an important trademark on M version of 1er. But let's wait ...
The car will certainly be M engineered but the question remains what badge will it wear. M? CS? CSi? Tii? GTS? That's on marketing dept. & management board to decide - just like it was in the case of 3er / 4er / M3 / M4 for 3er coupe & cabrio variants.
Expect an upgrade of 135i Performance Package + Power Kit ... slightly reworked in M way, offered in standard package. The most work will be done on chassis & ECU - to fit M character better. No revolutionary solutions in engine area though since the development time is very short.
It's more of an after-thought. They are considering to offer a limited edition of the car (limited production) - to spark a desire for next generation sporty 1er (ie "tii").
The next generation of 1er - based on new platform - will be made with a sporty version in mind, and not being limited in production numbers. Therefore the chassis will be much more capable than current one - which wasn't made for possible M version.
But don't expect cheap M car. This sporty 1er will be far from being cheap & affordable. Sure it will be cheaper than M3 but ...
Btw, Mr. Segler said no M7 & Z4M - only M versions of 1er, 3er, 5er, 6er & the X5/X6. Sure he can not talk about Z2 yet.

More then certain tech the (driving) character is important for M cars.
No M hybrids & M electro cars & M Hydrogen cars in the near feature - but the cars will feature certain EfficientDynamics solutions. Also no diesels: but there will be diesel models with M-packages which in the future will be more functional than cosmetic (analog to Audi S models).
Different M cars will present different characters - according to the customer pool & segment they are in.
Mr. Segler thinks an affordable M car (like 1er M) is much more important for the brand image then an M supercar.
It looks like M3 GTS & Performance Parts for certain models like 1er, 3er, Z will have to do the trick for more race-oriented BMW drivers. While M cars will even more focus on double Dr. Jekyll / Mr. Hyde role: being extremely capable & drivable daily car which can become an extreme sports car via M button.
Also: Mr. Segler says the mos important goal in M GmbH is profitability in line with BMW Group "Number ONE" strategy. Profitability being more important than sales numbers themselves. And that M has to be more dynamic & flexible than ever.