As someone who is new to the startup scene, coding ability is necessary, but the ideal technical co-founder would bring more to the table. A few thoughts:
1. Startup experience: Whether you're like me and this is your first time, or you have experience yourself, this is a huge plus. Everyone is better seeing situations a second time. Nothing is harder than the first time... the first packed bar if you're a bartender, the first patient you get to touch if you're a surgeon, the first crowd you stand in front of if you're a comic (it's been a winding path... hahaha). After your first time things slow down and you're not so overwhelmed. Big value add.
2. People skills: I'm not saying that I'm looking for the most outgoing guy in the room, but if all goes well, there will be a tech team to run and manage. From what I've seen, management is an extension of how you interact. If you're nice and considerate, you're likely to be a nice and considerate manager. If you're confident, you'll be able to make the right decision even if it isn't popular. Plus it'll be way more fun going to work every day with someone who is nice.
3. Curiosity: This may be because I'm in a complicated space (healthcare) but I want to work with someone who has a desire to learn. It's key that team members speak the same language. And the only way that will happen is if they both want to learn.
Just my two cents....