I found this board, from a guy in Japan. I’m not gonna pay $25 for this, however it’s a start at making the Teensy into an easy to use interface. What else does this need?
https://www.tindie.com/products/freto/teensy-3-breakout-board-and-shield/
The nicest thing about that one, for me, is it provides easy access to the pins that live underneath the teensy 3/3.1. As for “need” - that’s a pretty widely open ended question there, isn’t it? 
“need” for what?
(and that is why I mostly resist the temptation to try to make an “ultimate controller board” or whatever
I gave up on the ‘ultimate’ board, however, this is a great hybrid, for Arduino and Teensy. I haven’t really seen anything like this. I love the Teensy, but why does it have to be so teensy?
Are you kidding? It’s size is a large part of the reason why the teensy 3/3.1 is still my go-to controller for led projects. It’s small enough to easily embed in all but my smallest projects. The arduino boards (forget the megas) are often way way way too large for anything i’m doing.
Affixing a teensy 3.1 to one of these though, to use as a prototyping board at home might be interesting and useful, though.
What I meant to say, is that I could use all the Arduino Shield stuff I have lying around, on the Teensy quite easily with this. The positives of embedding the Teensy in your projects, is another post for sure
I dont think this one has access to the bottom pins, and doesnt look as nice, but way cheaper!