Indeed. Modafinil is already a somewhat popular study drug, so there may be no major increase from any price drop - not that I know how one would quantify uptake since college surveys tend to be one-offs...
There is a huge black market in Adderall at my college but, to the best of my knowledge, none in Modafinil.
Modafinil is now being covered by at least one insurance company in Massachusetts under which it costs less than $1 for a 200 MG pill. I predict a huge college black-market trade in the drug.