2. We can build our own plugins
3. It's not impossible to translate or emulate existing VST plugins.
And yes, you can build your own plugins. You cannot replace the thousands upon thousands of VSTs out there. You aren't replacing, for example, RealStrat, which is a supersampled virtual instrument, without re-recording the entire thing (do you know how? Is anyone going to bother doing it when they can use existing, conventional software?) and simultaneously reverse-engineering the algorithms used internal to it. You aren't replacing even something comparatively simple like an Amplitube without heavy-hitting, lots-of-money algorithmic research in the first place. (And, on top of that, I sure wouldn't want to deal with the patent encumbrances!)
And pardon my skepticism, but emulating latency-sensitive, CPU-intensive stuff like audio processing strikes me as a pretty foolish idea. When milliseconds count, your emulation layer just gets in the way. What benefit are you bringing to make additional failure cases and additional latency worth a user's time?
You aren't reinventing the entire audio world; as with many other fields, the lingua franca is C and not you and no matter how much you yell at the mountain the mountain's not gonna move. If you want to play, you have to play with (good metaphor for music in general, now that I think about it). Maybe you should rethink some of your decisions, or better constrain your ambitions. Because right now--and this may sound harsh but I'm saying it because I like seeing people succeed--it sounds like you're doing the software engineer That Guy thing and handwaving away difficult things because they aren't conducive to the postulates you're starting with.
I'm also quite sure that an audio program with a plugin architecture will be feasible in Zeta, once it's more mature. The system is built for scripting, multi-language support and dynamically loading packages. It will be an excellent platform for plugins. You'll be able to define your own custom plugin language(s) easily, and then you'll be able to dynamically browse and load plugins from the package manager.
When you compare yourself to LLVM, you phrase the comparison as only an advantage (Zeta will be easier to use than LLVM), rather than a tradeoff (Zeta will aim for ease of use before performance, as opposed to LLVM).
I don't suggest that you start hedging your writing, but am just pointing out that if you make big comparisons, people will assume great ambition on your part.
As previously stated, my goal with Zeta is not to replace all existing VMs and to satisfy every use case. It's an experiment, it's an opinionated system. I'm going to do things differently from other implementations and try to demonstrate interesting things along the way. Even if Zeta never becomes popular, I know it will make people talk, and I hope it inspires other systems.
I'm not telling you not to have opinions, to be clear. I'm suggesting maybe you shouldn't adjust those pince-nez and pronounce so hard. Many systems exist the way they do for reasons that Software Developer That Guy cannot divine from outside; you just happened to hit on one that I know a little bit about.
(Photoshop is another example; professional-level tools require professional-level expansion. Because everybody's definition of "professional" is different.)
In the audio space, it is vital to support FFI for a plugin architecture because I can guarantee you your language isn't the-best-thing-since-sliced-bread for somebody who has stuff you really want available to you. Audio software lives and dies on the VST specification. (Audio Units are substitutable for VSTs--but the same problem remains.)
I admire your efforts, but perhaps you should understand the use cases of the things you want to use as examples before you try to employ them. It doesn't instill confidence.