I spotted my first pedelec fat bike yesterday, which also just happened to be a KTM Macina Freeze. Whilst I still don't personally like them, and probably never will, I can see why they appeal to those living close to sandy beaches, boggy ground where low ground pressure is required, or in snow. I can also see that they would appeal to someone that wants to stand out from the crowd, and have a bike that could be customized to the hilt. I'd also imagine that the ride would be very soft, compliant, and forgiving, which might also appeal to someone that specifically requires that kind of ride for say joint pain issues.
I don't know about the price aspect though. Taking the Macina Freeze as an example, I think that it costs about £2,700.00 Clearly the cost is nearly double that of the E-Rex, but if I was in the market for one, and the E-Rex fell within my price bracket, but the Macina didn't, I still think that given the higher component spec etc of the KTM, I'd hold out and save up further, or take advantage of the 0% finance that some dealers offer. The problem with that opinion is, that I am already a couple of bikes down the line, and my requirements now, are different from when I first started out.
I guess that the only way to find out if the bike would sell, is to get a couple and try. It could be a case that like other cheaper bikes, it is a way to get someone onto the pedelec ladder, and from there, in a year or so, they would or could upgrade if they so desired. I know that there is arguments for and against lower budget bikes, but if they get someone else out there riding, then good luck with it.