tldr; 'watchpoints' in python can do this already(since before clojure existed), but it's not built into standard pdb.
You could do the allocator yourself with a custom allocator easily. Just inspect the object type or object id, and in your meta allocator select the correct allocator.
I'm not sure how that would help you with a CCL style WATCH though...
pdb, with set_trace or conditions on breakpoints could let you WATCH individual objects. Search google for watchpoints.
Congrats to the python-core team and thanks to everyone for another great release!
[0] http://ccl.clozure.com/ccl-documentation.html#watched-object...