Around my lab we eat up USB to Serial adapters like candy. I embed one in just about every microcontroller board I make, either as part of the core functionality, or just as an easy diagnostic and bootloading tool.
Sometimes exposing the mini-B connector is the way to go, but I keep finding myself wanting to permanently attach a short length of cable ending in a USB-A connector. To do this I’ve been removing the mini-B socket and soldering wires to the pin pads, but this is cumbersome and the results can be a little flimsy (hot-glue strain relief to the rescue!). On the older adapters I used to be able to solder some of the wires to plated through-holes in the boards, but on the newer boards with the pins labeled (nice!) the through-holes are covered in soldermask or something and hard to connect to.
So, I would be really interested in a USB to Serial adapter with the four USB lines brought out to user-accessible pins. A second pair of GND and VBUS pins isn’t absolutely necessary, but it would be nice. It could just be the next iteration of the USB to Serial adapter board, maybe offered with or without the mini-B connector installed. Or even just one version with the connector, I’ve gotten pretty good at removing those guys when I don’t have space for them.
-Adam