It would be nice if CAT could be dragged kicking and screaming into the 21st Century with control over USB rather than an RS-232 cable. The only people I know who have come close to this are Icom with the IC-7600 but I'm willing to be proved wrong.
I think there might be some others... I guess the Elecraft K3 can have a USB to serial inside the case?
Yeah I just keep buying USB-to-TTL-serial adapters and using those... here's one all done up with the adapter close to my Kenwood TS-440S. http://n3ox.net/files/kenwood-cat.jpg
One issue is compatibility with useful legacy equipment though. If you have an ordinary serial port on the back of the radio, $15 and some wiring can turn it into a USB serial port. If you just have a USB jack and want to hook up your old amplifier that sent and received CAT commands without a computer in the mix? Good luck.
There's no real reason why you couldn't offer both on the back panel, though, and built-in USB would be nice.
I would love to find a way to add CAT control to my homebrew gear. The three DDS chips in the rig are already under microprocessor control but I have no idea where to start.
Did you write the code for your microcontroller? Does it have a serial port? I haven't done a ton with CAT yet but I have set up an Arduino to request frequency information from Ham Radio Deluxe (should be straightforward with any microcontroller with a serial port)
Here's some Arduino code to set the frequency of a DDS module (from Ebay, essentially identical to this http://www.ebay.com/itm/DDS-Signal-Generator-Module-AD9850-0-40Mhz-Sine-Square-Wave-/321057477882?pt=LH_DefaultDomain_0&hash=item4ac08454fa
but from seller ci_tynight209) http://n3ox.net/files/sketches/serial_interface_AD9850_0_2.pde
and here's some code that talks to Ham Radio Deluxe to read frequency (and in this case set a pattern of lines on a shift register for station control, emulating a parallel port used for antenna switching etc)http://n3ox.net/files/sketches/parduino_v_1_1.pde
It's been a long time since I played with the second code.
A proper combination of those two would be useful to, say, synchronize the frequency of the AD9850 DDS with another radio. That's actually a planned thing here because a CAT-controlled radio synchronized with a signal generator and a soundcard input can make for a pretty useful scalar network analyzer
But I haven't put both of those things together yet.