The thing is at the moment heat pumps add high costs, and due to the UK climate, it is not a necessity that is needed,
The biggest win on the HS PHEV is the 75 mile range, which is one of the best for PHEVS and the best for under £40k
I totally agree that the major deciding factor here is price. This model of the MG3 unlike its predecessor is designed for a global market, and while some parts of that market might benefit from a heat pump, the cost of fitting one would reduce profit margins and push the base price perilously close to its main competitors. The car's main selling point is its low price compared to its main rivals, namely the Toyota Yaris and Renault Clio hybrid.
Much like Suzuki, MG is looking to sweep up loyal followers of the Ford Fiesta and Nissan Micra. These customers may not particularly want the SUV offerings of those particular Margues, preferring instead to stick to a supermini. The price jump to the Puma or Juke is also a deciding factor, and let's face it, the price was the main selling point, for the majority of us, and for that price, you get a reasonable car with just a few quirks. In my case, in SE trim, it was 6,000 euros less than the entry-level Yaris Hybrid. If I had opted for the Trophy model, that price difference would still have been 4,000 euros.
Interestingly, Suzuki in looking to keep their prices down, opted only to go the mild hybrid route. They could well have looked at partnering with Toyota in much the same way that they did with the Swace, but that would have left them, very little wiggle room in terms of pricing and placed them on Par with the Mazda 2 Hybrid.
The other deciding factor is where they would MG squeeze in a heat pump, given that everything is crammed in as it is, with the auxiliary battery relegated to the wheel well and the spare wheel left on the shop floor, for the hybrid version. The petrol version of the new MG3, holds on to the spare wheel as there is enough room under the bonnet to take the 12v battery.
The problem of where to fit everything into a supermini is not a new one. I remember back in the day, my first cat, a Fiat 127 had its spare wheel under the front bonnet over the engine bay.