Personally as a fellow free software developer, I take whatever opportunities I can to look closer at what value the software is really providing for the user. Is your primary user actually interested in the freedom and community the software provides, or are they just looking for "Pro Tools on GNU/Linux" with a low price tag? It's probably a combination of the two for most users, and as you have found there is tons of tweaking that can be done to optimize for the middle-ground. I personally choose to lean more towards optimizing for freedom and community, but the downside to this is it requires more infrastructure to support it.
From the download page it looks like your anchor point is a one-time $45 for unlimited upgrades. This is already fairly cheap for DAW software, but I would be interested to know which of your pricing options actually does generate the most revenue. That would probably give you clues as to how to build a stronger free (gratis) version that doesn't reduce overall value for the user. Subscriptions being popular means you can probably consider paid add-ons and services. User wants to use proprietary plugins? It's added maintenance costs, make them pay for it. One-time purchases being popular means you probably need to pursue sponsorships. Unfortunately I don't know a good way to do this at scale without either A) embedding obnoxious advertising, or B) finding generous corporate benefactors. Everyone obviously wants option B and option A sucks for everybody. Whoever can find the equilibrium in between these will get rich.
I also want to add that I tremendously respect what you're doing and how far you've come, and that I probably would not be a musician if Ardour did not exist :)