I can see a direct drive hot end being modified and Arduino'd to make the ultimate 3D Pen!
Then you can probably print Peek if you wanted for far less money than a bonafide super duty 3D pen

Otherwise I have no idea of what is out there for performance pens. I played with one of the toy pens my sister had and the performance was less than mediocre.

What about a modified glue gun that can take either 1.75 or 3mm filament using a manual feed? Okay just an idea.