Quote: "Will FPSC:R directly support old model packs (especially EAI's weapons)?"
Not directly some changes will need to be made to the fpe file in most cases. The best place to find out information on how to do this is in the Models and Media board.
Quote: "Will FPSC:R support projectile-based guns or it will stick to hitscan ones?"
This is not confirmed but I am sure it will be added in a later version the engine is certainly capable.
Quote: "Will FPSC:R feature fixed gun emplacements (usable turrets) for player and AI?"
You could do this with clever scripting even if it is not an actual feature, might be an idea to add this as a feature request as no one I know of has asked for this yet.
Windows 7 Pro, Intel i7 3.8 GHz, 16GB DDR3, NVIDIA GTX 780 4GB Superclocked