Shawn, if you think about it, lots of helicopter accidents occur at very low airspeed due, for example, to inadvertantly being downwind, getting into vortex ring or just running out of power. Whether you are doing 70, 80 or 90 kts IAS is of no consequence but whether you are doing 10, zero or -10 is much more important. So its a pity that conventional ASI are accurate in the unimportant range, and inaccurate or in fact non-functional in the important range!
This is why the CAA did some research into a low airspeed algorithm based on control positions, accelerations etc being derived from a neural net type programme. I seem to recall that a lack of reliable "learning" data was the stumbling block that stalled the research.
What sort of system were you thinking of, a mechanical vane-type or a synthesised / algorithmic type? If the former, the kit can be more of a hazard than its worth!