No external power brick for power source. I hate those things. Built in power supply with built-in short term battery backup would be nice. It would only need to keep it running for few hours.
Other than that, I'd like to have it simple. 2 PPS, 3 10Mhz, Power indicator, 1 PPS indicator, RS232C/USB, and big UNLOCK alarm LED, and a reset button. I really don't need an LCD.
I'm actually on a fence on RS232C or USB. Most PCs today no longer come with RS232C. It is also starting to lose compatibility. DTE/DCE was bad enough. Now 3.3V, 5V, and TRUE RS232C involving +/- 24V. USB may be a reality, and since we don't use that for timing, I'm not sure if it's a bad thing. If it was for NTP feeding pin9, I would be against it.