Marius,
Perhaps we're lost in translation. I have no application installed on my router that needs tunl0, until you released ampr-ripd v2.3. This is important because this -L argument could cause issues in the future.
My device *only* routes traffic, so no application uses tunl0 except the -L argument of ampr-ripd.
*I've never needed to assign a OSI Layer 3 address to a PHY not used on Layer 3.* Only my 44bridge and 44 devices use 44IPs, and they all use tunl0. Only they sit on tables that use tunl0, and the rules point to those IP and interfaces to use...table 44! Those routes use tunl0 ONLINK. If you ping my device br-amprnet responded, everything worked as you described, except no IP is necessary, until you placed Layer 3 into ampr-ripd.
- KB3VWG