This is in the “would be nice” rather than “essential” category but I think it would helpful if pop up dialogs in PceEmacs, specifically the Query replace dialogs, could be dismissed with the Esc key.
Added, though the Emacs abort (^G) already worked. It makes the editor a little nicer for non-emacs people though. Also added the Emacs screen split/join shortcuts to Epilog (^X2, ^X3 and ^X0).
Further support for mgondan’s tenth rule: Any sufficiently complicated piece of software contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of the Emacs editor.