There's also the cacheing of the compiled bytecode of *.tcl pages beneath the www/ pageroot using ns_cache, which Rob Mayoff implemented in
aolserver/tcl/tclcache.tclin 3.3+ad13. That's not in 4.0 yet either.
However, that's a performance issue only, everything will work without it, and it would probably only be important for high volume sites. (So far, no one as really characterized the performance difference.)