Seeing that we have some modelers making good progress on unique clothing, I think its the right time to start discussing the first steps we need to take to get modular clothing to work while using a minimal amount of assets. This is important, as even unique clothes contain elements that could be used as our "generic" bases for clothing types - such as underlying robe shape. Figuring this out now, and modularizing even our unique assets will save us time and effort in the long run.
Nexos and I started discussing by clothing type, the minimum number of "base" assets we'd need to achieve the variety we would like when paired with modular pieces/textures/colour changes. We've put together our first attempt at this below and it is very much open for debate, especially by those with 3d experience.
To be clear here, the idea is that these "base" assets will work as the literal base for the modular pieces to be built on top of, saving us the effort and also establishing size standards to help the chances of clipping when mixing and matching. This is a pretty important step to do. EDIT: because of this, even if we have say 3 robe variants, they should stem from the same archetype shape and then be given their unique flare, so that the modular pieces can fit more often on all 3.
See the spreadsheet here
FUTURE STEPS (to be discussed later)
2. Once a base number of assets is decided upon and during their creation, the concept art should be sifted through to find concepts that would work with a given "base" model type and then the modular components will be identified by concept to make it easier on the modelers. Quick concept modifications could be done to help with the potential implementation hurdles.
3. Once all concept art is assigned to a "base" model type (if it can be), then the modular pieces should be discussed based on the pool of artwork available. Discussion should occur about the different variations that can be achieved with texture changes, or if more concepts are needed to fill in holes/rework designs that varied too much from the base models.
4. Modular pieces are created and then implemented with different textures/combinations to achieve variety.

i have much to add to this, but so little time, hopefully the artists we have can help with this modular stuff in a couple of months.
THere are some things to start now though.
Lets hang soon.
I have a huge PSD file that could be a proposition of sorts, feel free to try different combos out. You can mix and match many layers to create gondoliers, miners, farmers, townsfolk, netchimen, thugs, fishermen and many other, even smiths and trainers. If I ever get enough time I'll export some archetypes.
http://www.mediafire.com/download/znz9y6h6tgwjaif/DunmerClothing.psd