My thoughts on the current skill system:
1. Perception and Acrobatics are just as much forms of defense as AC or hit points. Perception is the defacto threat detection skill.
2. Since clearing dungeons invariably means negotiating an obstacle course, Athletics has slightly higher importance than most other skills.
3. Tool proficiencies: Playtest time was focused on the top priority of D&D, which is adventuring activities. As a result, these are mostly for background and affording daily expenses, save a few notable entries.
4. Knowledge skills: They kept the knowledge skills limited to what needs to be kept track of for adventuring, and that is a good thing. It's a bad idea to try to quantify too many areas of knowledge in a skill system, since it denies the implicit knowledge that comes with many skills. If you have tool proficiency with thief tools, you know something about mechanical devices. So does a locksmith. Including a mechanics knowledge skill would just complicate the system. Again, a really good choice on their part.