Since your goal is to channel water away, why not use the very light, but water repellent fabrics available from Thru-Hiker, DYI, Titanium Goat and others. That's around .66-.8 ounces per square yard. You want lots of vapor permeability to limit condensation, but also water repellence to keep the moisture from dripping through. Since one is usually a trade off with the other, the sellers mentioned above are pretty good at giving you an idea of how they are balanced in each material.
The only problem is these are all or mostly all nylon fabrics, and they will sag considerably when the cold and humidity increases, and limit your headroom. Don't know how silk performs under these conditions - if you do, please post.
I'm a little leery of Velcro's holding power when it's wet, especially with small Velcro dots holding something up against gravity seeking to peel the Velcro open. You could try the thin plastic rectangular loops used on watchbands, sewn with twill or grosgrain tape close to the outer shell, and then run Velcro tape sewn to the liner through the loops and back upon a piece of Velcro sewn flat on the liner to get the attachment as close to the outer shell as possible and cut down on the loss of headroom. With mitten hooks, you would get more distance between the shell and liner.
You might note that many tentmakers are using .7-.8 ounce insect netting for this. TarpTent is, and Franco might post about that. They seem to feel that the netting is sufficient to stop water from condensation (not from leaks) from dripping onto you. That has been my experience also, and I agree. So I'm looking around for polyester netting in the same weight range, as it will probably have much less sag than the nylon.
After thinking about this issue a lot, I also agree that something is needed to stop the drips, and protect the occupant and gear from rubbing against condensation in single wall tents, DESPITE the weight penalty. So it may be, that it makes more sense to just design the liner into the tent. But if you already have a single wall, or really like a single wall on the market, the liner would be needed. Someday, we will have ultra-light material for tent walls that passes water vapor but keeps water out. In the meantime, some form in inner will make the tent much more comfortable. Couldn't agree more.