I mentioned before that I hate the progressive research cost system. It makes that early research are too cheap, while later game research are too expensive.

I think it would be better to replace the current system with static research cost and turn the research matrix into research tree like in many 4X games, where low level research would be cheap and high level research would be expensive and would requires some ofther depending research.

However to make it true tree we would need more type of research, so here are some ideas:
Ship fuel efficiency 1,2,3,4,5(each level needs previous and is more expensive - recude the amount of fuel the ships consumve when trave.
Ship travel speed 1,2,3,4,5 - speed up the ship travel speed between sectors.
Station fuel efficiency 1,2,3,4,5 - all stations that use fuel use it more efficient (less fuel per production cycle)
Ship types produced in Shipyards should be research - e.g. first you need to research light corvette, then heavy etc.
Each station locked by research should be now separate research - more advanced stations are higher in the tree.
Research efficiency 1,2,3,4,5 - works like the current, reduce general research cost of all technologies.
Additional weapons and ship ugrades - each should have it's own research.
Repair speed 1,2,3,4,5 - increase the speed of ship/station repair.
Small haproons, Big harpoons - allow the ship capture, need to research small before large.
Additional lineral boosters 1,2,3,4,5 - allow rapid acceleration or deaccelaration (to full stop) for your ship (useful when you speed too much or need to boost into one direction) - consume fuel so the number of usage is limited by level.
Ship armor 1,2,3,4,5 - makes ships more durable, but decrease accelleration and agility
Ship thrusters 1,2,3,4,5 - increase ship agility, useful when combined with additional armor
Ship Engines 1,2,3,4,5 - increase acceellaration/deaccelaration, useful when combined with additional armor.