Surprisingly, the only non-conforming thing I could find with the assembler is support for numbered registers. For example "mov 1,2". Now that's been fixed. There are of course a lot of E/A specific keywords having to do with code location and linking options the assembler does not support, but those don't make sense in this context anyway.
One thing I've wanted to do is get the -g option working correctly to allow mixed source and assembly output files. This would allow faster debugging and to quickly find code that turns into ugly assembly.
I added config options which should have allowed debug output, but any build done with -g crashes the compiler. Hmm.