That option exists today. The iMessage bridge needs to run on a Mac, for obvious reasons, but not only can you self-host it, but you can plug your self-hosted bridge into the public homeserver/client entirely through their settings panel.
Here is the bridge repo: https://github.com/mautrix/imessage (tulir is employed by Beeper)
The disadvantage of not offering an API for iMessage is that there is no easy way to block clients. Apps like Bluebubbles have to work by being installed on an actual Mac and scraping messages from iMessage and Beeper uses a similar architecture[0]. Presumably they have a data centre full of actual macs (or VMs).
You can self-host with https://github.com/mautrix/imessage and https://github.com/matrix-org/synapse/
I know how crazy it is in America, but I think at leat the HN crowd wouldn't be participating in that madness.
If you are disparate enough, you can use a matrix bridge to get blue bubbles from anywhere
I have an Android phone and if you're desperate you can buy an old Mac Mini and set up an iMessage bridge over Matrix (https://github.com/mautrix/imessage) or BlueBubbles to work around this. I do not recommend it though as it locks you into a facet of the Apple ecosystem.
https://github.com/mautrix/imessage
That's the bridge Beeper uses. I've got it running on a 2011 MacBook Air on MacOS 10.13, almost zero issues.