I'm not big in the audio community but I thought LV2 was the open standard for plugins that people are pushing for? That being said if Cockos adopts it into Reaper I'm absolutely willing to try it.
It also never got enough support from big guys. Clap looks like it fixes a lot od LV2 stuff as well, and it can replace VST, which is good because VST is a crap technology.
First is the licensing. VST2 is hard deprecated and not possible for new businesses or developers to target it (* it is possible via some reverse engineered header files but they are GPL licensed, which turns people away). VST3 has an awful license.
Without getting into the weeds too far, VST2 is pretty easy to target without a bunch of work. VST3 is pretty much impossible without some kind of heavy wrapping technology (even the bespoke distribution doesn't use the API directly, it wraps it in a heavy and confusing SDK - most people use JUCE, IPlug, DPlug, or the other wrappers anyway).
Also VST3 doesn't really support MIDI (1 or 2). They pretend to, by making the host do the work to translate MIDI into VST3-specific API calls (which are tricky to keep sound, makes it a pain in the ass for host and plugin authors, and is generally a terrible design) - search for JUCE authors trying to understand why their MIDI plugin isn't working in VST3 (it's because VST3 can't do that, and Steinberg won't accept that plugin authors and users want to be able to do it).
Lastly, VST3's i/o configuration for multichannel audio is a nightmare to try to understand and arbitrarily limited in a way that can't be expanded easily. It added a ton of complexity for no benefit over VST2.
The fact that its taken nearly 15 years and legal action to get anyone to support VST3 for their plugins is ultimately the biggest indictment against it.
It is licensed under two licenses. One of the is the GPL v3 or later. Evidently you don't develop libre software, and additionally dislike the other Steinberg license.
VST3 for all its issues was the first version of VST usable by the libre software community - VST2 was not legally re-distributable even though it was available gratis. This prevented legal development of any libre VST2 plugins, which was not a good situation for anyone.
I have multiple projects licensed under GPLv3. The biggest request I have gotten has been to relicense them so closed source projects could use them - which I would be fine with, but I'm not actually free to do that because of upstream GPL dependencies.
There are other legal issues with Steinberg and the licenses, particularly the recent changes (some of which are contradictory and the language needs adjustment). But if you're not a developer of a well known project, Steinberg will ghost you. The devs are kind, but unhelpful, and legal is unreachable.
And ultimately, users don't care about libre software. They care about software that works. That's why VST2 was so popular despite the licensing situation, and why DAWs that supported it are DAWs that people wanted to use.
correction, SOME users don't care about libre software. I know I didn't for a long time. As my concern grows about the unsustainable consumption we take for granted, and its deep environmental and social impact, libre software has been getting more and more important in my life. A ten year old desktop PC can meet all my computing needs - but it seems that's only true when it's running software that was developed at least partially separated from profit motives.
I would go further than this, I'm interested in audio programming and decided to give it a shot using the Steinberg's SDK after reading the VST3 docs. The way the SDK is organized put me off VST3 entirely.
Sort of. The breaking of MIDI is not, by any means, a good API. In a few other aspects it seems needlessly complex - feels like it was designed to serve one company's strategies and interests, not that of an industry.
It also never got enough support from big guys. Clap looks like it fixes a lot od LV2 stuff as well, and it can replace VST, which is good because VST is a crap technology.