On Hardware side the support for 5.x is not bad, Nordic Semiconductor for example is quite fast in adding support to their stack, and the updated stack is avail

On Hardware side the support for 5.x is not bad, Nordic Semiconductor for example is quite fast in adding support to their stack, and the updated stack is available for most (if not all) of their chipsets. That said, even if a company which already launched its product would upgrade their stack to a newer version, it's unlikely that they would spend the money and resources to re-certify for a newer BT-version unless there's an explicit need for it. They rather treat this as a maintenance release of the existing certification... So it might be that there are more devices with 5.4 BT-stack out there than it seems...