[Guruman]

one of the biggest PT drawbacks, and something that would be a drawback to your initial concept as well, is the fact that the number of hole cards used to create the hand is not distinguished.

for example, a hand like 33 on a K77 board would end up defined as a two pair non-drawing hand, but it would play dramatically differently then a K9 on the same board.

Also, in headsup play Qhi unimproved has showdown value, and Ahi has can be bet for value unimproved. One is not necessarily "drawing" with all kinds of hands that you would initially classify as "drawing".

Further, hands that are drawing are often only drawing to pair up so that should be included amongst your "drawing" categories, as it's the most common one.

Also, how would your system deal with multiple draws?

I think that you should definately add a showdown unimproved consideration into the equation. Some hands are made preflop even in limit holdem, and will have no intention of folding.