Aside from the Leica mount lenses, there could be many old gems that could still be usable on the upcoming A7/7r. Of course, only real testing would show how useful they might be.
Here is a list (based on checking with projection on a GG and in some cases on my Leica MM) of probables:
First E mount lenses (not really "small" but I thought I will throw them in ):
1. 30/3.5 Macro (needs to get rid of rear baffle)
2. 24/1.8 (rear baffle has to go)
3. 50/1.8 (ditto).
4. 18-55 (possibly from ~28mm onwards)
Olympus pen F lenses (not sure of the corners!):
5. 70/2 (no worries)
6. 100/3.5, 150/4
If you anything to add, feel free.