Well, if its just your friends you could make a small minimod to make slow even slower, no devs required.
Go to your steam app data folder and go to Rebellion. In the folder with the .exe files, you should see a folder called GameInfo. In that folder go and copy a folder called Gameplay.constants.
Then go to your my documents folder. Go to my games, Ironclad Games, Rebellion. You should see a bunch of folders for saves and also a folder that says Mods-Rebellion v0.90 or something like that (or whatever version you're running). In that folder make a new folder called "Slow Mod" or whatever, then in that folder make a new folder called GameInfo. In that folder paste the Gameplay.constants file.
Open your copied gameplay.constants file in notepad and look for the lines below. By reducing the numbers under the "slow" label, you will make the associated features even slower. You might want to make the changes one at a time because I'm unsure if setting things like buildSpeed or income to negative will work, but after say lowering Research speed to -7.5, save the file, start rebellion, go to options, and the mod tab. Enable the mod and hit apply changes, and your checksum should not be zero. You should now notice research takes longer. Repeat with the other catagories until they become slow enough for you, then zip up your "slow mod" folder and send it to your friends and enjoy your super slow game.
buildSpeedData-Slow
shipBuildRateGameSpeedScalar 0.0
moduleBuildRateGameSpeedScalar 0.0
buildSpeedData-Normal
shipBuildRateGameSpeedScalar 0.10
moduleBuildRateGameSpeedScalar 0.10
buildSpeedData-Fast
shipBuildRateGameSpeedScalar 0.20
moduleBuildRateGameSpeedScalar 0.20
buildSpeedData-Faster
shipBuildRateGameSpeedScalar 0.40
moduleBuildRateGameSpeedScalar 0.40
cultureSpeedData-Slow
cultureConnectionReferenceLength 250000
allegianceShiftRateScalar 0.75
cultureSpeedData-Normal
cultureConnectionReferenceLength 500000
allegianceShiftRateScalar 1.0
cultureSpeedData-Fast
cultureConnectionReferenceLength 750000
allegianceShiftRateScalar 1.25
cultureSpeedData-Faster
cultureConnectionReferenceLength 850000
allegianceShiftRateScalar 1.45
researchSpeedData-Slow
researchRateGameSpeedScalar -4.75
researchSpeedData-Normal
researchRateGameSpeedScalar -1.3
researchSpeedData-Fast
researchRateGameSpeedScalar -0.15
researchSpeedData-Faster
researchRateGameSpeedScalar -0.05
incomeSpeedData-Slow
incomeRateGameSpeedScalar 0.0
incomeSpeedData-Normal
incomeRateGameSpeedScalar 0.15
incomeSpeedData-Fast
incomeRateGameSpeedScalar 0.30
incomeSpeedData-Faster
incomeRateGameSpeedScalar 0.75
fleetSupplyData-Small
fleetSupplyScalar 0.75
fleetSupplyData-Normal
fleetSupplyScalar 1.0
fleetSupplyData-Large
fleetSupplyScalar 1.25
shipPhysicsSpeedData-Slow
shipLinearMaxSpeedGameSpeedScalar 0.0
shipLinearAccelerationGameSpeedScalar 0.0
shipLinearDecelerationGameSpeedScalar 0.0
shipPhysicsSpeedData-Normal
shipLinearMaxSpeedGameSpeedScalar 0.30
shipLinearAccelerationGameSpeedScalar 0.30
shipLinearDecelerationGameSpeedScalar 0.30
shipPhysicsSpeedData-Fast
shipLinearMaxSpeedGameSpeedScalar 0.45
shipLinearAccelerationGameSpeedScalar 0.45
shipLinearDecelerationGameSpeedScalar 0.45
shipPhysicsSpeedData-Faster
shipLinearMaxSpeedGameSpeedScalar 0.6
shipLinearAccelerationGameSpeedScalar 0.6
shipLinearDecelerationGameSpeedScalar 0.6
victorySpeedData-Slow
diplomaticPointsRateSpeedScalar 0.66
occupyVictoryTimeScalar 1.5
victorySpeedData-Normal
diplomaticPointsRateSpeedScalar 1.0
occupyVictoryTimeScalar 1.0
victorySpeedData-Fast
diplomaticPointsRateSpeedScalar 1.33
occupyVictoryTimeScalar 0.75
victorySpeedData-Faster
diplomaticPointsRateSpeedScalar 2.0
occupyVictoryTimeScalar 0.5