Let me just first congratulate tyran_nick on this mod! Great work!
I like the idea of making human equivalent of plasma weapons. My own thinking behind it, as probably shared by many, is that humans - although capable of comprehend aliens technology - due to lack of biological diversity among human races, are not able to implement Plasma Technology in field weapons in the same manner as aliens do. Thus it is required to invent weapon better suitable human physical characteristics, that are capable of delivering comparable punch to plasmas.
I've come across two mods already introducing diversity to plasma weapons. Chico's New weapon graphics and Shadow's Terran Plasma Weapons. IMO Human's Plasma should place somewhere between Laser Weapons and Alien's Plasma. Mass Accelerator weapons in this scenario could've been crown jewel in human arsenal - lightweight, with better accuracy than Alien's Plasma and only marginally slightly less power.
I think that in this light tyran_nick's mod adds quite a lot to the game. Not only by making larger research tree (slower progression), but also adding diversity to human arsenal. As always devil is in the details, so some tweaking would be necessary to balance all weapons altogether. I love the idea nonetheless!
Further I think introduction of this mod with Terran Plasma Weapons would effectively balance the game by making aliens weapons totally useless. I'd love if ex. alien weapons could've been dissasembled in workshops into Allien Alloys and Ellerium, and on top of that, making any Human Plasma Weapon would require Alien Weapon equivalent (Human Plasma Rifle would require Alien Alloys, Ellerium and Alien Plasma Rifle) - with logic behind it that although size and shape of alien weapons makes their use by humans impossible, some of their components can be use to produce human's equivalent.