I've read a few things about a brakes upgrade and a suspension upgrade in some old posts and news articles. Has anyone heard anything else about those or are they just rumours?

 

You can try to email JCW directly and ask the question. I know that they have many other upgrades for the MINI that are not sold in the US. So far only the upgrade kit for the MCS is sold but later on more might be coming. I would say what you suggest is still rumor.

If you want suspension and brake upgrades done by a good company that offers warranty then wait for DINAN to release their line beyond the announced Stage 1 and 2 upgrades for the MCS. Any upgrade for suspension and brakes for the MINI should work on either the MC or MCS and would likely come in stages just like everything DINAN does.