I agree with Neal that the division isn't going to do much if you keep the "other part" as an allies section.

My suggestion would be that you start by paring down the LatD list to a pure "cultist" list (the background for the old LatD list is that is a the Stigmatus cult, a big cult that has started an uprising). I think a good list needs a focus, and the Stigmatus Coven is perfect.

Some ideas for that:

- The cult has access to captured imperial tanks and other vehicles, but they're disorganized and not present in large concentrations. Add infantry to Leman Russ and Basilisk formations, but reduce the number of each type (so, say 4 Russes and 6 infantry, and maybe 3 basilisks and 3 infantry). The cult doesn't have dedicated armor formations, but rather large mobs which have managed to capture some tanks or artillery pieces. Combine Rough Riders and Sentinels into one formation (2 or 3 units of each). If these mixed formations are found to be a bit weaker than formations of just a single type, reduce the points.

- Move the daemon engines into another list that features them. They scream "from the eye of terror" to me, not something a cult on a hive world slaps together. A cult has secretly taken root and now they're suddenly emerging into the open - with Questor Titans and Lords of Battle? Really? Replace with daemonically possessed vehicles (could be a character upgrade like I put into the traitor pdf list I threw together).

- Maybe add a "technical"-type vehicle? (The trucks with machine guns they use in africa.) LV, some with a heavy stubber, some with a missile launcher. Upgrade to a Coven, or maybe in a new formation of 6 infantry in Land Transporters and 3-4 technicals.

- For air support you have Hydras and Marauders, but how about a formation of daemons that use Fighter rules? By the rules they're simply Fighter Aircraft, but for models and backgrounds they are flocks of daemons summoned at the start of the battle to attack enemy aircraft.

The question might be that should the Cultist list be named as a Daemon Engine List and the PDF list renamed as the LatD list then we can concentrate on that list to get something workable?

& I have no problems with Daemon Engines suddenly appearing on worlds, they are big places and you don't know for how long they have been there, being constructed, being worshipped. What I don't want to do is to end up having the Daemon Engines restricted to SM Cult lists.

IMHO a cult would have imperial hardware, but not imperial organization. My suggestion for mixed formations is one way of showing it, but there could be others. A cult would have many IG units, but not anything resembling IG formations. For me it's totally fine if the diffferent formations means that the units are used less effectivly in-game. The Imperial Guard should be better at using their own units, after all.

Ah, so you are thinking along the lines of an Ork style army list.

So like:
TRAITOR GUARD MOB - 350 pts
Three Leman Russ, One Hydra, and eight Imperial Guard Infantry units.

The way the lists are now split up are to allow current players to mainly keep their current lists but with more focus on one of the two aspects.

Us oldies from the Space Marine era naturally do this anyway I suspect. Certainly for me, it's very rarely a fifty-fifty split, so the system you've implemented here seems unnecessary to me.

Furthermore, new players could just decide to use the units which they can easily get their hands on, rendering both the split and percentage system somewhat redundant in my opinion.

And that is what we must remember that we are not just working on lists that are for us old guys but also so that people can get into the game as well. I would like to see more people playing LatD but most of the 'fun' units are too expensive for people to start off with without spending alot of time converting or ebaying.