Why not add an LSM memtable on top of the cow b+ tree?
Use the skiplist as a write buffer and write to the b+ tree in batches when the skiplist is frozen.
In-memory immuatable data structures seem to be only suitable for scenarios with large amounts of data and high concurrency. In most scenarios, this actually incurs a lot of additional copying overhead.
Why restrict it to Shell programs with script language? What about LLM powered chat? Terminal is the UI between humans and machines, future is IM App. What people do to each other, people and machines will do the same(ask,talk,chat,assign task).