I just came from Best Buy and they have a few Motorola phones that work with Boost (CDMA compatible). To name a couple, there's: Motorola - MOTO G (4th Generation) 4G LTE with 16GB Memory/32GB Memory;
and emory/64GB Memory
You may check all Motorola phones on their website here: click on each phone to check the description to be sure it is compatible.
CDMA phones that work on Sprint work on Boost. In the past, Boost wouldn't unlock phones. The law now requires unlocking. Since this phone comes unlocked, there's no reason why Boost can't accept it. Boost sells a Moto G4, in fact.
They don't let you bring it if it's unlocked. I have a Moto G1 that was originally a Boost phone which I bought from Boost and used on their network for a few years. I got it unlocked to try another carrier on the Sprint network. I didn't like that carrier much and wanted to bring it back to Boost but Boost doesn't allow it back even though both carriers are the Sprint Network. It's not the phone itself it's Boost's policy. Probably because they want you to buy a new phone from them.
You are right. The problem is with Boost policy. There are many phones that would technically work on Boost, but they just tell you that you cannot bring them. For example, I had a Google Pixel phone that I tried to bring to Boost. While I could bring it to Sprint, Boost would not allow me to bring it. So for those who might purchase an unlocked CDMA or Sprint compatible phone that should TECHNICALLY work with Boost, make sure you call and verify first. This is because they will likely tell you it's not compatible, even though there is no technical reason why it should not work. I agree, I think they simply do this becaue they want you to purchase a new phone. They'll let iPhones on their network, but I think that is because there are so many out there that they would be shooting themselves in the foot to not allow iPhones. Otherwise, they don't want you to bring a phone so they can sell you one.