OK so I played around with this for awhile and I have to say that while it is a nice idea, it has a few problems. This of course doesn't include the obvious power creep that this mod adds to SS, which is unneeded.
Extra system problems
#1: Most ships are BELOW normal quality (which defines how effective boosting with it is)
#2 Quality is not well defined. It is labeled on a scale between .5 and 1.5. Does that mean that Extra system would make the ship WORSE?
#3 RNG when applying upgrades. Just make this *** more expensive instead
#4 Extra system unpauses the game automatically when you exit out of the interface. Would like to see it like Console commands does it OR better yet, make it a station!
#5 Ships are rerolled with save transfer. This could be fixed with the ability to improve the quality of the ship
#6 You can upgrade more times with caps (25 times) then with frigs (10 times). This, combined with the RNG of quality makes it a pain in the hand to upgrade everything again after Save Transfer. Just make them all the same number of times and or allow us to make more than one "point" of upgrade
#7 Being able to upgrade anywhere is a bit OP