It is limited by what the world format can support, so as there are no changes to the world format in 1.7 you can still only have 32000 items (including 4096 blocks)
As I've mentioned in PM, it's the modpack's responsibility to ensure they have EVERYTHING needed for loading minecraft, even the libraries. That's our official stance, the change was done on purpose, and we are not going to revert it.
Fucking scala has caused more than enough fucking problems already. Anyway, fixed, URL changed. Download http://personal.forgeessentials.com/luacs1998/forge/fmllibsmc16.zip and extract that to .minecraft.
I can't help you then, our tests show that the files are perfectly fine. Why not try taking scala-library.jar from the zip and putting it in your mods folder?