My quick thoughts on the topic: I like the idea of combining the medicine proficiency with a healing kit to provide added benefit (stabilization using both raises a creature from 0 to 1 seems fair). The skill could also automatically give the character a free healing kit to as a practical starting incentive. I think you should be able to use the skill in any village/town to earn revenue or traded goods (and/or goodwill from the locals), particularly places where means of magical healing means are absent or expensive/difficult. It could be used in similar fashion in an adventuring setting to earn favorable disposition from any NPC in need of treatment. Making a check could determine efficacy of treatment given. Last, it could be a good way for a certain characters with healing capabilities integral to their character's personality to earn an Inspiration point.