1: The shiny particles have been increased since the 1.7 versions and shinies now have a golden name above them and a star in the battle UI. But none of the increases ever seem to be enough...
2: Asking for Pokémon additions here is blacklisted for a good reason: We will do it anyway, so there is no point in suggesting it.
The reason why the knockoffs are ahead is because they steal their models from the original games, including all the issues that includes. Our assets are created specifically for the mod, optimized for the use in Minecraft to minimize the impact they have on performance. And that work takes some time, especially since our modeling/animation team is pretty small.
We're always looking for people willing to help out in order to speed up that process.
3: Most comments I have seen on the legendary spawning system say they'd prefer if they were a bit more common, actually. So I doubt adjusting the defaults to make them rarer would do us any good.
That is entirely irrelevant though, since you can easily change the rates in the config to how you prefer them.
4: An overhaul of the battle UI is on the list of changes we'd like to do. But that list is long, so we can't make any promises on the time frame or order of these changes.