there are Writeable everywhere.
what's the benefit of home-made this?
and compareing to use some widely used s/d framework like Protocol Buffers, what are pros/cons?
Speed, size and backward-compatible-version support are benefits to hand-coded serialisation logic over generic serialization frameworks.
Cons are having to write the custom code.
so is there any plan or no plan to use third-party framework or home-make framwork rather than current status?
There is no plan to use any third party frameworks