I think quite a few people want to see Judy made
thread-safe. Ideally, this wouldn't be coarse locking,
but rather some mixture of techniques to minimize the
locking actually required. For example, you can often
get away with locking just writers and not readers.
Add in pluggable memory management and an easy way to
serialize the structure to make it persistent and/or
send it over networks, and you'd have the most flexible
data structure around.
The problem with a data structure you can use for
everything though is that it would be really tempting
to have more and more data stored in a tree of Judy
structures, but if you have to lock the whole thing for
every read, then the performance would be WORSE with
threads than without and multithreaded programs are