For the Arduino route I'd heavily recommend the Adafruit Bluefruit boards over the official Arduino BLE boards. Some of the Bluefruit boards are based on the nRF52 and therefore support OTA. The BLE implementation on the official Arduino boards (for example Nano 33 BLE) is okay but IMO Adafruit is doing a better job there.
The nRF51 and nRF52 OTA firmware upgrades also look usefull, has anybody done something arduino like with this?