This mechanic was not just a balance concern (although it was, in fact, a balance concern), it also was one of the production facilities for playstyles. One player could focus on getting the most units possible and that would be macro style. The other could play defensive, keeping his opponent at bay with constant drops and map control through threat not numbers (that playstyle, IIRC, was dubbed Yangachi terran and was practiced by UpMagic of the more recent players).
But medivac does both. It would be a cost-efficient unit even if it didn't have the ability to drop. It directly influences the power of your army. On the other hand, it provides drops essentially for free. Add in the capability to use a reactor to produce 2x medivacs from just one starport, and you will see the whole picture. The unit is broken, it eliminates playstyles (there's no point NOT to drop when you go MMM) and gives terran a significant edge in whatever TvP. Blizzard, however, cannot remove a unit from an already working game, besides, terran really needs both medics and dropships in some form.
So the solution proposed here is:
A unit produced from factory, costs 50/50, has 60 health/1 armor and 2,25 movespeed. Doesn't require tech lab. Mechanical/Light. Does essentially what medivac does, but being a ground hovering unit, doesn't fly or drop. The range of healing is 1 cell less than that of the medivac and maybe healing rate slightly reduced.
A unit produced from StarPort, costs 100/75, has 120 hp, drops. Replaces the medivac. Doesn't require tech lab.
An upgade in StarPort tech lab, allows attachment of Healing Drones to Dropships. Costs 50/50, researches for 1 minute game time.
Once Medical attachments are researched, a Healing Drone can permanently attach itself to a dropship, making it a medivac and giving it the ability to heal.
1) Medivacs are still in the game.
2) You cannot just get medivacs straight off the bat. In fact, to build them, you need a rather inexpensive upgrade.
3) You don't get both drops and healing on the same time for a small price.
4) If you still need drops, you can do them for the same price, which is not achieved when going the most obvious route of increasing medivac costs.
5) You can go a healing ground army without starport tech.
6) Eliminates the ridicule of Factories being so worthless that they are being used as a scouting suicide unit.