The current Skitarii list is not to E&C's liking because it doen't mesh with the story
Pretty much this. I stepped down so that someone else could develop a Skitarii PDF list specifically for the supplement, and the new Champion decided instead to develop a Skitarii Attack Force list, which is useless to the supplement even if it does get finished one day.
The new Mechanicus Champ. has also been changing unit stats, that will make it difficult to make the required defensive Skitarii PDF army variant list style (Ie: slower moving Ordinati are needed, not ones as fast as battle tanks) at some point in the future without having conflicting unit stats.
So, Vaaish decided not to develop the list style, the ERC backed up his choice to place priority elsewhere, and the supplement effectively got cancelled by the very action (my stepping down because I needed to take six months off to coincide with the birth of our first baby)
that was supposed to hasten its arrival. Ironic.
If anyone manages to develop a defensive PDF themed Skitarii army list at some point in the future (possible - there's a process going on in the Mechanicus forum to see if a new Champion is wanted), then I'll dust off my already-written supplement. If not, it's dead, 'cos I'm done with list development, I'm soured on the whole thing.