> How sure are you that the vendor is actually providing device-specific updates?

First of all, my phone runs an FSF-endorsed operating system, so no closed drivers. Granted, not everything has been upstreamed yet, but they're working on it and I trust that it will be done soon. (They have done it with the devkit.)

Second, my phone has removable modem and removable WiFi card (no unified memory), so when the firmware can't be updated anymore, the card itself can be replaced. (They actually have already done it by releasing a new WiFi card; 5G modem is also being tested). In the worst case, the device can still be used as a pocket computer with no wireless communications.