The eco sharing allowed by the Crotalus' mod stops at sharing mass and energy.
Would it be possible for two players to designate engineers or factories to be "shared"
which would mean that these engineers are now allowed to get resources from either player?
A similar situation can be achieved by setting sharing thresholds to zero using the above eco manager mod and then all units are essentially taking resources from both players.
The control over the shared engineers is open ended. If control is given to both players it really opens up the game to new possibilities.