To justify "officially" merging some GNU/Linux Live ISO image into UBCD, it has to be light in resources (low RAM required, low CPU required, low size required), updated tools, actively maintained, *easy* customization by additional modules (such as testdisk, clamAV,...), user-friendly GUI (specially the file manager, with easy access to different types of media and filesystems).
I guess you did not read gparted default list. File manager pcmanfm is included the exact same file-manager parted magic uses same basic interface to access different types of media and filesystems. Testdisk is also included. Next is ram usage is lower than parted magic.
Clamav and others can be apt-get in or you can rebuild with them included. http://gparted.org/create-gparted-live.php
Really a ubcd customised create-gparted-live is what I am more thinking of.
ady you say realistic potential candidates are few. Sorry realistic candidates in my point of view you are making impossible.
Dropping a Linux distrobution losing gparted so losing fully function partition editor is not even a possiblity. Without the partitition editor you have mostly bricked the disc for a lot of issues. UBCD was to solve carring around the 100+ floppies for different diagnostic items. Objective is 1 disc.
syslinux.cfg of a debian live cd will be just as bendable as a parted magic one. Creating the tool to process gparted iso thinking its iso is a standard debian live cd covers clonezilla and many others.
The most common tool disc are debian live.
pmagic/pmodules stuff is in fact horible you are fully dependant on upstream to update. Its not hard to script a equivent to pmodules without half its limitation issues.
Gparted iso module files are just standard .deb files. Read the create-gparted-live its using a gparted disc on a system with 1 G+ of ram to rebuild itself. You can apt-get any extra tool you need from any debian repository with gparted live as long as you have the ram to hold it. Note you can apt-get any extra tool you need.
Add apt-offline to gparted and you are in party central. http://apt-offline.alioth.debian.org/
apt-offline runs on Windows OS X and any Linux distrobution with python to make new bundles. Yes the result of apt-offline is all dependancies include for requested program to add in 1 file. Yes add a .deb package that adds a check somewhere for apt-offline files and order their install and you fairly much have what parted magic is upto.
So moving to a debian base you can rebuild your addons on Windows and OS X with the latest versions.
apt-offline is not the only option once you are inside debian.http://listaller.tenstral.net/
this is the other. listaller produces IPK files that are fairly much distrobution netural.
So ady choose path of replacement to parted magic modules. Both of the replacement paths provide advantages.
Sorry I don't see parted magic as something particular great or special. Both IPK and apt-offline bundles have their advantages and leave parted magic modules in the dust.