Depending on how many uses the medpaks have, I doubt the issue of medpak usage limits will play a major factor in the game. In the original X-Com, medpaks rarely ran out (of course, that's because soldiers rarely survived getting shot). If medpaks have a limit on the number of uses, players will simply carry more medpaks. Although I imagine coding the medpaks to have a limited number of uses is fairly simple, it doesn't seem like a major issue.
Now one thing that is major is how medpak healing is handled by the game. If the damage healed is permanent, then nobody will use hospitals. If medpaks don't heal enough in missions, then nobody will use them, chosing instead to use their turn (which is basically how long it takes a rookie to apply a medpak currently) for something more constructive. It seems that the current system is working well, with medpaks taking roughly two uses to restore a soldier's health from half to full, and the healing not being fully permanent. Still, the newest version has only been out for two weeks.
