Unfortunately, CDMA is locked by design, so it isn't possible to offer such a version in the Play Store.
I'm sure there are a lot of reasons Ting went with Sprint (probably easiest to deal with), but I think if they were a GSM carrier then they would be an instant success and game changer. Many people have a hard time dealing with paying full price for a phone, want to bring their own, or don't like the selection. Being a GSM carrier generally takes care of these barriers.
Also, LTE isn't as critical with HSPA+. Sprint and Verizon 3g is a joke compared to it, which is why they need LTE.
I don't think it is reasonable to expect this kind of pivot from Ting, but I can dream, right?