Forgive me for possibly being rather naive, but surely if the number of auto or AWD sales is likely to be, at best, a handful a month, then surely the corresponding number of relevant spares that would likely to ever be needed would also be proportionally low, so any additional cost of stocking of them would be significantly outweighed even by the potentially few sales that would otherwise be lost by not offering those options in the first place?
The value of AWD specific spares stock required for a handful of AWD cars would not be significantly less than the value required as back up for the several thousand non-AWD cars that MG will be hoping to sell. The value of AWD specific spares stock that would be required would be massively disproportionate. Due to the low margin on new cars now, it wouldn't take much extra outlay to outweigh the small extra return from selling a small number of extra cars (look at the MG3 - it has a list price little more than the MG ZR did at launch 15 years ago!).
Ask Land Rover, Suzuki or Skoda if AWD sells. Or do MG just want to have no USP other than built in china and cheap.
With Land Rover in particular, you are looking at a different sector of the market. The CS appears to be targetted at the lower end of the SUV market - aimed directly at the Qashqai, and there is little demand for AWD at that end of the market. The volumes that MG are likely to sell do not justify offering the AWD version. I would expect that if the CS sells well beyond expectations (ie. perhaps 10000+ a year), and 5% of potential customers say they want AWD, MG Motor would be likely to market it here.
On performance so far, I think we have to come to terms with the fact that the bulk of the British car buying public doesn't want to buy the current MGs, and no amount of advertising, special discounts, number of dealers seems to make a significant impact. Whilst we all hope it will sell in thousands, I think you would have to be very optimistic at this stage to assume that the CS will fare any better.
There may be other reasons for not offering AWD in Europe - possible safety or emissions related issues which may need further work; who knows? (well, obviously MG Motor will know, but they are not likely to say in public).