Congratulations on the new R Andy. I'm late to the party as usual 
I look forward to your updates.
My 135 is 4 years old this year and the PCP will be due to end so I need to do something but really detest this stage approaching dealers etc. 
The M135i is one of three cars have in mind for my next change which will be coming from a 128Ti
Have really enjoyed the 128Ti but it does have a couple of drive irritants.
The comfort setting can make the gear box lazy at times, times its perfectly seamless, then you randomly have a little hesitation, which has me keeping it in Sport most of the time. - Have you experienced that in the M135i or should I ask for that to be checked at next service.
Torque steer is real, and in front end just does not give you full confidence in the wet on B roads, so I am backing off way more than would like to, though in straight line and dry its a super quick and agile FWD hot hatch. - Really want to know if the AWD kills all these issues?
There is nothing else do not like about it, the cabin feels premium and the media and O/S is top notch, though i would definitely be seeking a Kardon Harmon specced car as sound is pretty average, and the only other thing would change is the drivers display map, its next to useless when compared to the inlayed map on the MK 7.5 Golfs for example.
Would probably find and pay the little extra for the performance pack and 19"
And to Andy question, what next if moving on from the M135i? My quandary is would like to have a MK 8 R or Clubsport but it would have to be a early to mid year one, and just cannot bring to risk myself issues, and the MK 8.5 which think like more and would hope would have the issues removed, is way beyond my budget, so that's really limited me to late MK 7.5 Golfs or the M135i. As much as like and enjoying the 128Ti it just falls short overall, and if stayed FWD would be seeking out a GTI PP or TCR as the drive is just better.