I have recently came up with a couple fun subfactions. I thought I would put out some guidelines for what constitutes a sub faction as opposed to a whole new faction.
1. A subfaction should consist of one currently produced faction with only a few, if any, units from another faction.This is so people who don't own every faction can take advantage of the subfaction.
2. The main unique flavor should come from different faction abilities.This is so there are as few actual changes to the cards as possible.
3. It is certainly workable to change a units status from standard, core, or elite, to something else. For instance, the Frost Dwarves have Hammermen as core reflecting the great profundity of ice-picks in regular use.
The goal and art of creating a subfaction should be to create a unique feel to a subfaction while retaining as many of the physical components intact as possible.
I decided to do this because, while there are some really great ideas for new factions, they often languish because they require all new components and that is a lot of trouble. To fill in some gaps I thought we could try some similar but different "subfactions."
You can view my first attempts here: http://gullsbattleground.blogspot.com/
I'm sure others can do better.
The other advantage to YMG is if a subfaction proves to be popular it could stimulate sales of the parent faction and that's just good for all of us.
I've changed my spelling from sub faction to subfaction so it doesn't look like we're building U-boats!