First let me welcome you to the forum, next the Hdd driver is finished for fat16/32, it come's as a loadable module or built into the kernel in the next ver.
http://dex.7.forumer.com/viewtopic.php?t=185
As for dead no its very much alive, i am working on a dashboard(gui) and will be releasing the next ver of Dex4u in the next week or two which will include built in hdd driver, fully skinable gui, etc.
http://www.dex4u.com/images/Dash4u.jpg
There is not a day that goes by that i do not add some code to Dex4u.
It would be great if you port your code to Dex4u, as for others adding to the kernel, i try to do most of that work, so it's compatable, but any one with source code can add improvements and if they work well, will be added to the main ver (as the code is available to all forum members and i will PM you a link to the code).
Now theres a module interface, anyone can add drivers to the OS.
As for testing Dex4u programs, theres a iso
http://www.dex4u.com/dexiso.zip
you can burn to cd-rw.
and this is recommended for emulators
http://www.dex4u.com/DosBoxDex4u.zip
NOTE: these are not got some of the latest things, but will give you a idea.