TL;DR: a Mk2 repair pack, and a few researches to increase repair speed
slightly longer version:
this would add a few researches, one of them being the unlocking for a mk 2 repair pack, which would have more health, and repair faster, and after that a few researches that increase the repair speed, but only a low percentage.
a possible specific configuration we came up with would be
research 1: 'advanced repair packs' would require 75 for red, green and blue science, unlocked after advanced electronics, this would unlock repair pack Mk 2/advanced repair pack, and would cost 2 normal repair packs, 1 steel plate and an advanced circuit to make 1. it would have 600 durability (double of a normal one) and a repair speed of 3 (50% more than normal one)
research 2: 'faster repair 1' this would give a repair speed boost of 5% at a cost of 100 packs of red, green and blue science
research 3: 'faster repair 2' this would give a repair speed boost of 10% at a cost of 150 packs of red, green and blue science
research 4: 'faster repair 3' this would give a repair speed boost of 10% at a cost of 200 packs of red, green, blue and purple science
research 5: 'faster repair 4' this would give a repair speed boost of 10% at a cost of 300 packs of red, green, blue and purple science
research 6: 'faster repair 5' this would give a repair speed boost of 15% at a cost of 400 packs of red, green, blue, purple and yellow science
Yes, unless you use rocket silos as defensive walls, I struggle to see cases where a faster repair pack would be of much additional benefit, nor do I see compelling reasons to make the MK2 repair pack over more MK1 repair packs. The speed of repair is never the limiting speed of anything in factorio.
If the MK 1 repair pack only healed things to half health, I could see a possible niche, but otherwise, no.