Some simple shortcomings of VST and other formats:
- Dispatcher uses fixed "opcode" indices and data structures
This one isn't a really big deal but it does make the API needlessly complicated. Features that aren't needed in most cases are stuffed into the code of every existing plug-in. The methods used are easily extensible but a lot of risk is associated with making such extensions: once adopted they are very difficult to replace or remove. This could be fixed via existing methods for handling extensions. More on this with #3... - String handling uses limited fixed-length strings; not suitable for UTF-8
All functions and structures associated with strings should pass a pointer and length. No fixed arrays. - Meta-data associated with most data elements is for the most part redundant or obsolete in most cases.
For example (related to #1) being able to associate XML-like markup with parameters, presets or other elements would allow something like "category=filter", "widget=knob", "color=blue", "tags=fat,bass,analog". This data could be ignored entirely but in hosts which want to categorize presets or neatly arrange GUI widgets into sections or pages by group it would suddenly be possible. See CSS for example... - Notes and parameter values aren't possible to associate with voices. There is no concept of polyphony or voices. It isn't possible to interpolate parameter changes and they are instead limited to block edges.
Self-explanatory in my opinion.
They decided to abandon VST2x and implement some of these (partially) in VST3 and just look at how widely supported that format has become: not very widely at all.
So it's clear that these features and others are not nearly as valuable to others as they are to me.
If you're not willing to tell anyone about what you want to see implemented; the odds of it being implemented are zero. Just flat out not going to happen.
If you want to simply say "hey I've got this idea for this feature, it works like this: ..." and give comparisons to demonstrate the shortcomings of existing formats vs. the benefits associated with the feature you'll only start to climb the very first speed-bump: being acknowledged at all. Being accepted as a "good idea" is the next step and that cliff-face is very steep and free of footholds.

