Just to add a bit of an insight as a person who basically gave up Linux Audio almost entirely due to the lack of plugins.
The problem, in my opinion, is not in the format itself. The way I see it, there are 3 major problems, in no particular order:
1. Lack of documentation and tools that would ease development for LV2 and JACK support.
I could, without being a programmer, put together an audio program or even a basic plugin when on Windows. On Linux I couldn't even get started - it is very complex programming and even setting up JACK is not very simple at all. Of course, these are the words of the non-programmer, however, it does say something. Besides, I am not the only one pointing out the lack of documentation and tools for rapid development. A JACK library that would allow to setup JACK support in an application easily, like JACK_Init() would be great, but atm it is not even close to that.
Of course, this point is the weakest point I bring up, I am understand that as a non-programmer I might not make sense here.
2. Most good plugins on Win and Mac are not just proprietary, they are commercial and their producers offer them for pretty high prices.
It seems to me that most serious VST and VSTi programmers are ready to go into audio development only if they are sure they get paid handsomely. At least, on Linux we have Zyn and now also Phasex, two only serious VSTi-like synths, which get ported all around, while in the VSTi world the amount of synths of such quality and options is more than 2. In fact, much more. Many serious DAWs come bundled with 2-3 of them at the very least and come with a dozen of standard effects like Delay, Reverb, Flanger, Chorus, Phaser, Compressor, EQ, usually of pretty decent quality. On Linux Audio I have difficulty finding a reverb and delay that suit me, CALF being the closest to a good delay.
I don't know if money is the only factor, but it is very much on the surface, the difference in the offerings.
Also, there is a whole bunch of decent freeware VST plugins, but as far as I understand this very much depends on what I said in problem 1 - I know several people personally who had made pretty cool effects and synths of a level that is a rarity on Linux, assisted by plugin making tools that ease the development a lot, including GUI development.
3. Not a lot of people in the Linux Audio world seem to care much about that particular type of music that requires a lot of synths and fancy effects.
On my site I wrote an article which many people have probably read, as I referred to it often, which makes a distinction between two types of music from a production point of view (http://www.louigiverona.ru/?page=projects&s=writings&t=linux&a=linux_types).
It seems to me that this, by far, is the most important reason Linux Audio does not have a lot of plugins - most musicians (many of them being developers at the same time) here simply do not need them. They record their guitars and vocals and are pretty happy. And those people that do need lots of fancy plugins, come to Linux, hang around, see that nothing is in the store and leave.
Again, I think that this is the main reason. If a lot of people would be here who need a delay plugin with many options or a serious reverb or whatever - it would pop up. Atm - I don't get a sense of that need. And last year when I was very actively researching what Linux Audio can offer, it seemed to be I was the only person who talked about electronic music and the need for fancy effects. Obviously, I am not the only one in question, but I am part of a very minor group, that's for sure.
Cheers!
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Louigi Verona
http://www.louigiverona.ru/