Color TFT type LCD backlit display
Touchscreen + a few hard buttons and 2 knobs (Volume and Squelch on separate knobs!)
TEXT search! Need to find something, simply type in a few letters and be presented with a list to select from....
Ergonomic controls that work consistently. If a button works as mute, then put "MUTE" on the dang button. No secondary use (Fn) of keys other than upper and lower case text. No special "codes" or "Quick keys" to remember to operate the unit. Use a simple menu structure based after Garmin devices or Apple devices. DO NOT use a menu key on the side, Func key above that, a knob on top, keypad that is not labled for what the buttons actually do... (you know, like the BCD396xt!) which forces you to operate it with 3 hands. Keep it consistent!
Customizable display: Let us decide what is displayed during scanning and searching, and where, and with what fonts.
Make the text on buttons and on-screen menu's either LARGE enough for old people to read OR customizable screen display fonts.
Lithium Ion battery pack with contacts on bottom to charge off a drop in docking station. You can also include an AA alkaline battery adapter, leave off the charging contacts on this adapter so it can't be "charged" on accident when dropped in the charger with non-rechargeable AA's installed.
Include multiple receivers, so Fire Tone Out can monitor more than one frequency simultaneously. This would allow for monitoring several dispatches (FD + EMS + ...) simultaneously
Bluetooth so we can use wireless headsets
Just a few off the top of my head.....