40K did sub-factions in a way of pick a faction then paint your army in a certain way and that becomes your sub-faction. This was pretty good, but did have some flaws. The main flaw was if your sub-faction's focus was doing bad you just really lost. Now you could say 'hey I'm playing them as blah blah' but this always couldn't work. With 10th edition they changed it where sub-factions for the most part are now detachments, with most if not all are inspired by a sub-faction from before, but now you can choose them no matter how you painted your army. This is good but it has lost a bit of flavour to them, however one army list still has sub-factions in a fair enough way, the Space Marines (Guard also but ya Space Marines were like this from 10th start). Simply some epic heroes and units have an additional faction keyword. I think a big release of epic heroes (and non-epic hero units for some) is the right way on going about this. Thus be on the look out for this going around, I'm going to be sharing once I have most of a Faction's sub-factions down. This is 1 named character from the lore that hasn't had a model, or whose model needs a refresh and/or a return. Along with a non-epic hero unit. This can be a character, a squad, or even a vehicle. If you feel you know for your faction you like and/or play please share this with it.