I've thought about that acid stuff before, and I even tried to implement it, using the Vepar_Impact ani from the mv_(adv)effects.vp file and a modified weapons, ships, and impacts table, and it worked acceptably. The problem was that I couldn't figure out a good launch mechanism, and that it dealt damage in exactly the same way that the other weapons i modelled it after did. It is a neat idea, and I'd like to be able to use it, but I would have to work around these problems to do it.
The other thing about an acid weapon is this: Either I would have to balance it with other weapons, or I would have to make it a significant part of the campaign, but doing both would be difficult. I'm looking for something like the Shivan shield technology, but different: I want something that can be absent at the beginning of the game, can be captured/developed/obtained somewhere in the middle of the campaign, and can be a balanced addition from that point onward. This actually sort of applies to all weapons.