It isnt a solution just to enable all research topics for all players. That is boring.
I think i have got i nice solution for this problem. I suggest a completely new research philosophy. Think of a list of research topics with their corresponding costs (research points) next to them, like this:
Turret X 100
Turret Y 60
Turret Z 40
Research Upgrade One 50
Research Upgrade Two 80
...
Now lets say every player finds a button in the multiplayer menu in future saying "My research topics". Each player has 10.000 research points which can be allocated to different research topics. The points are not enough to get all research topics. You have to decide which technologies you prefer!
In the game the research topics get automatically researched by your research facilities. A higher number of research facilities increases the research speed (like it is currently).
I hope you understand my suggestion

