There are several things that make this difficult. Much of the difficulty relates to the device changing it's network address. Seamless transition requires that the application can:
- Find the new address; i.e. Cell provider vs. Residential/Business ISP
- Associate the new address with the same flow
- Duplicate packets and reassemble them, or change to "better" path interface.
On both android and iOS, a regular app can't choose to send packets over both 5G and wifi at the same time. Thats needed to setup a new connection while still using the old one.
- Find the new address; i.e. Cell provider vs. Residential/Business ISP - Associate the new address with the same flow - Duplicate packets and reassemble them, or change to "better" path interface.