If you use a noise-cancelling microphone, to avoid interference from surrounding noise, the concept isn't so far-fetched. Both Windows and Mac have good enough speech recognition to recognize simple phrases like "Gear down", "Flaps up", etc.. The trouble would be the interface to your transmitter. I'm sure it could be done, but I don't personally know how to wire it.

This is interesting. If someone will help you build the device, we might all be interested in the future. Maybe an RC manufacturer will take the lead, by building in some simple software, and a microphone input. I hope someone helps you accomplish this.

The important thing is the noise-cancelling microphone. You don't want the scenario of someone walking up to you and saying "Man, I just can't get my "GEAR UP", and watching your plane collapse onto the runway. It's probably best to have a "push to talk" button on the system, so it only listens when you're pushing the button.

Good luck.