There's probably no wish to monetize, just to distribute working apps for free.
You're right that the issue is easily addressed with a proxy.
But now you need to maintain and pay for a proxy in perpetuity, for other people to use who aren't paying anything.
Even if it's cheap, maybe you don't have the time. It will break occasionally. Knowing there are people who may depend on it 24x7x365 is burdensome too. You'd like to have vacations.
It's not very open source friendly if other people can't just take your software and run it themselves without depending on you.
Those other people can avoid depending on you by registering themselves with FCM, but having to do that is not open source or self-hosted friendly either, which was the GP's point.
There's probably no wish to monetize, just to distribute working apps for free.
You're right that the issue is easily addressed with a proxy.
But now you need to maintain and pay for a proxy in perpetuity, for other people to use who aren't paying anything.
Even if it's cheap, maybe you don't have the time. It will break occasionally. Knowing there are people who may depend on it 24x7x365 is burdensome too. You'd like to have vacations.
It's not very open source friendly if other people can't just take your software and run it themselves without depending on you.
Those other people can avoid depending on you by registering themselves with FCM, but having to do that is not open source or self-hosted friendly either, which was the GP's point.