I'm not really familiar with the vim code base. From the little I've seen I'm astonished that people are actually willing to voluntarily work on it.
Having said that, googling revealed a bug report[1] where one of the main neovim developers states he would rather avoid "messing with a very obscure part of the C code." So yes, it seems to be difficult to implement into the existing code base.
There exists a plugin which adds some features, but because it is not supported by the editor core (hence the above emphasis on "native") it isn't properly integrated with other plugins etc.
Having said that, googling revealed a bug report[1] where one of the main neovim developers states he would rather avoid "messing with a very obscure part of the C code." So yes, it seems to be difficult to implement into the existing code base.
There exists a plugin which adds some features, but because it is not supported by the editor core (hence the above emphasis on "native") it isn't properly integrated with other plugins etc.
[1] https://github.com/neovim/neovim/issues/211