Gaylon,
To some extent, it sounds like you're talking about the NU-701. But it has weaknesses. Among other things, it's not small enough to ride on your belt well, the base units are not at all weather resistant, and they operate on a very limited frequency range, and are very susceptible to interference -- especially from other NU units.
So far the suggestions have been (1) Grill capable probe and leads. A thing you may have planned for already.
support a variety of probes
(2) Easy access jacks, (3) More robust weatherization (actually the ET-73 is pretty good). And (4) better access to controls. The screw on the back of the ET-73 is a bit of a pain.
All of these ideas are good ones, IMO. I'd also like to see (A) Easier programming for the alarms -- the ET-73 will only allow you to program in one direction. (B) Automatic search when the signal is lost. The ET-73
usually makes you turn the units off and on to reacquire a lost signal. (C) Leads sealed into the probes, so the probes can be easily cleaned. "Dishwasher safe" would be ideal. (D) Keep the remote unit small enough to carry on a belt clip.
Given all of this, including a four probe capacity and three included probes (1 (1000 deg) grill capabple, 1 meat, 1 chamber), I'd be willing to go a couple of hundred. But considering that's the price of 5 ET-73s, I'm not sure how many other people would. And, as JB pointed out, there are a variety of systems already on the market -- many of them wi-fi networked -- which means the user can use a smart phone or wi-fi PDA as a remote. FWIW, you could order a "Stoker" base unit; add a cheap access point; pick up a 12 V power supply from Pep Boys, and for less than four hundred -- there you go. Hell, with a repeater you could probably get 1000' of range.
Which leads to another consideration. At the price point a limited production run will put you in, you'll be competing with the Stoker and Guru. You may want to consider fan-bellows control as well.
Lots to think about. Good luck and keep us posted,
Rich