Mustang a very bad chassis???????

Have you been reading motoring magazines of BMW test pilots complaining about the live rear axle??
It's actually a very, very good chassis (from the front seat mounts forward, it is shared with the RWD Jags) it's just that Ford continued to use a live rear axle because when they did the market research all the current owners said they wouldn't buy one unless it's got a live axle.
It actually handles a dream (if you know how to drive a RWD car that hasn't got stability control - all BMW owners press the back button now please) but needs to be treated with respect.
Any production figure below 250,000 units per year is classed as a niche model.
This is why manufacturers sell multiple cars off the same platform.
At peak Capri sold 250,000 units worldwide (71-74) then dropped to around 100,000 units when it was removed from USA.
It's peak sales for UK was 83,000 which steadily tailed away to 25,000 per year in the UK only from 1984. It wasn't sold in any country other than UK RHD from October 1984.
In it's last full sales year (1985) it sold 19,000 units. Which was not enough for Ford to warrant production even though they made more money out of those 19,000 than they did on the Sierra's 150,000. It even sold 15,000 in 1987 long after production had finished and once the 280's price was reduced.
All they had to do was put the Pinto EFI egine in (which SVE were pushing for and ran proto-types of) and sales would have gone back over the 25,000 mark and it would have stayed in production.
The Probe sold 4,000 units in the whole of it's career, so you can see why it was dropped quickly.
You may love the new one but that new one (as I said earlier) is the 3-door Focus not a Capri.