I really want to use it but anything beyond the simple example is difficult to migrate to.
I must have read the toolchain pages 10x times but still setting up a custom compiler or even different JDK setup is confusing.
From what I have heard, the toolchain story is being worked on heavily. There are some legacy reasons why toolchains were designed the way they were (mostly due to the fact that Google essentially only uses one compiler for each language, and certain toolchains were implemented natively instead of as plugins), but the confusing semantics are improving! Maybe give it another shot in 6-12 months.