Raspberry Pi has a very close relationship with Broadcom, the once arch enemy of Qualcomm. The chances the next Raspberry Pi will be based on a Qualcomm chip is less than small. Also Snapdragons are expensive and documentation is hard to obtain and requires a lot of NDAs.
That is not to say the chip is bad, in fact it has many good things going for it that I would love to see in the next Raspberry Pi expected early next year such as powerful DSPs, ISPs and GPUs that can drive modern high resolution displays.