Hm, I wanted to create a threat about this [well transports actually, and the uselessness of the MKII], but I’ll add it to this one instead, I think it’s still new enough to be relevant:
MRS (Mobile repair station):
I think either the MRS knowledge needs to come down just a tad (2.5k? 3k?) or else the repair rate needs to be upped a bit (2x instead of 1x?) . I do find them useful (at epic combat speed) in really large fleet battles (we're talking 2k+ ships, that is full Mk I/II/III/IV caps of at least the triangles + 3 bonus ships at normal ship sizes). In encounters that large (and that slow at epic), fire is disperse enough that repair stations will get an odd few seconds here and there to repair fairly large numbers of ships. Engineer Mk III's also lose their value in this type of situation. Things tend to get too chaotic and they end up biting it rapidly and repeatedly in the bullet storm.
I guess the MRS are an unlock specific to a fleeter or else someone who has/uses significant numbers of crowd control ships (riot 2 tasers, Tackle drones, etc.). Large battles are still fairly uncommon until the very late game, for example when I'm trying to simply destroy the AI strategic reserve from 100/70% -> 0% without resorting to warheads.
In my opinion, MRSes don't really 'turn the tide' of a battle. If you are outnumbered or outgunned, you are going to die anyway. MRSes to me seem to be a macro-extension tool; that is they reduce the repair and replace cost of your fleet. If you know you'll win, you simply win with fewer casualties, allow for faster replenish, which helps with the less tangible operational and logistical longevity. If you come in with too much overwhelming force, MRSes are useless as there is nothing to repair. If you are going to lose the fight, again MRSes are again useless [unless huge amounts of CC are employed]. It is only in a very specific area: you are going to win by some margin, that MRSes help adjust the margin more in your favor. The total benefit is logistical and economic rather than direct combat impact. Your force can continue to move, and will need to spend less time/resources replenishing. MRSes, therefore, are really only applicable if you are in an attrition war with the AI; a type of fight many seem to avoid.
Transport MKII:
As to transport MKII's, I've never seen the need.
Here's an interesting idea: the Transport MKII can heal very slowly (when not being hit) in enemy/neutral territory. Balance it so it takes a minute or two minutes to heal the 'damage' a hop causes. If the transport is hit by weapons fire, it has to wait the same cool down as any other unit before the (slow) self-healing kicks in again. This will allow Transport MKII's to have higher effective range, but means that the player has to pay attention to microing the transport, and that the ships inside effectively cannot be used while in transit to their destination. You'll need to bring cloaker starships along to cloak the transports, or else be running them around out of fire for long enough to regen. In either case, you'll have to wait somewhere until they heal. This allows you to operate small groups of 'gruella' forces that can stay hidden, but cannot simply 'move' from out of supply system to out of supply system at a whim.
Transports or the units inside them should still trigger deep-strike threat if you go in deep enough to trigger it normally.
This non-trivial change would have a number of interesting effects:
(1) allows you to use the trans 2's to operate in 'hostile' territory that is not in deep-strike. By healing the units inside of it as well as itself, it can operate as a guerilla force in out of supply areas (e.g. jumping back and forth between two planets that are just out of supply as needed, without having to stop by a ‘friendly’ world first).
(2) allows you to transport-strike deeper: this would be accomplished by hoping 2 out of supply, healing, hoping one more, healing (still no deep-strike, on the edge now), and then doing 3 hops at full health as fast as possible, exploding. That's a 6 hop total (+2 from current transports), but had a micro and time cost, as well as a 'put planet(s) on alert cost' if you had significant units in the transports, with minimal deep-strike threat.
(3) Allows for 'super deep strike' (of theoretically unlimited planets), if the player is willing to continuously build threat while the transports and the units in them are 'idling' and waiting to heal. Eventually the raw amount of threat will likely just kill the player, in addition the fact that the ships inside the transport are essentially dead weight firepower wise for the entire time they are being transport (which is lengthened very time the transports need to stop to heal.).
Overall, this still leaves the transport MK II a fairly niche item, but it would open up some interesting possibilities, and justify the high knowledge cost of a planet and change.
One last interesting thought about this change: If you want to reduce the micro surrounding this type of thing, have the MkII transports have natural cloak also. If you want to keep it more micro intensive for the more ‘complex’ deep strikes, then force a cloaker starship to come along (and die) in the ride.