one can significantly reduce the memory footprint by using ttrace. ttrace does not produce the large "blueprint" of all (used and unused) tcl procs, but builds an index instead and the unknown mechanism of tcl to load tcl procs (and xotcl methods) on demand. according to zoran, it can reduce the memory footprint to a third and improve the thread startup time by a factor of 50.
there might be some fiddling around with introspection commands (e.g. info args procname won't work, when procname is not already loaded on demand; up to some degree, ttrace tries to handle such cases) and similar issues. i tried it some time ago with xotcl, where it worked nicely; we do not use it on our production site, where we see no memory problems. ttrace is part of libthread 2.6 or newer. for a pointer, see
https://openacs.org/forums/message-view?message%5fid=313348
