It would be possible. I'm thinking of adding "pack/unpack" operations to the Leaf data structure, but it's more motivated by getting a varint encoding for line breaks; right now each break is a 64 bit integer (on 64 bit builds), so if you have file consisting of empty lines, the corresponding line break data structure is 8 times bigger than the text. With the varint encoding I have in mind, it would be bounded at 1/4.

That said, I'm very skeptical that lz4 on text would be worth it.