In fairness, this is different to JCG of old.
As you point out, Cooper were the masters of branding, but it was controlled from their end. Going out and sourcing parts from others / outsourcing part manufacturing and possibly ideas is simply business.
The Cooper reputation was grown by being amongst the best, and by being linked directly to the manufacturer meaning it was likely easier to gain insurance, not void warranties etc.
The difference here is that a company that already produces conversion kits is re-branding their gear to gain sales / publicity / trade off the old reputation...
I'd bet that Mike Cooper was approached by MS rather than deciding to collaborate with them.
As a comparison, I'm also a Lotus Elise owner. I own a non-standard Series 1 Lotus Elise.
I could source and fit all of the parts that would convert my car into the limited edition, more desirable, and quicker Sport 160 Elise - a car which I believe Janspeed also played a part in developing, or even Series 1 Exige BUT my car would never be worth the same as an original one, and that's where this falls apart.
An original Cooper S, whether it's a Mk1, or a late MPI will always be worth more than a replica one in the same condition, even if the replica has all the right bits sourced.
For me, the question is, do these new MiniSport based Cooper kits represent the same as buying an original Cooper S from JCG, or is it simply a marketing ploy to shift units.
Each of us will have a different thought on the answer, and value the new 'S' cars differently too - either way, they absolutely WILL sell kits!
Chris