@tokumaru: For exomizer, just using $2006-writes is not enough, I tried... The algorithm would sometimes need to "read" from CHRRAM and sometimes from ROM. I don't understand the algorithm good enough to know when the input has to be switched. But I think it would be possible.
@tepples: Yes, modifying CHRRAM on the fly is a nice-to-have. Anyway, optional direct decompression to CHRRAM would be nice, too.
The compression ratio degrades with small intermediate buffers and splitting data into small chunks is complicated...
The drums? Hm... Ok, maybe I will give the DPCM-split a 2nd try when I have some time left before the deadline.