Well Ed, since your talk is tomorrow night (unless you mean NEXT Wednesday), you didn't leave yourself much time here.
That said, to me it's kind of like adding another forum topic: If folks don't pay attention, what's the use of an additional forum.
Likewise, it's easy to go to a train meet or an auction site, where trains are listed as mint yet are obviously used. Or like new, and they're covered in dust. Adding another category to grading standards will not make people become any more accurate or honest about how they perceive the condition of their trains.
Obviously, today's trains have more electronic features, and therefore have more that can go wrong. To me, and I agree, the current grading system seems to have a visual implication first, and yet the functionality is not excluded. If something is LIKE NEW that means it not only LOOKS like new, but it also operates like new.
I can see where some confusion could arise with categories below "like new" on the grading scale. "Good condition" implies there are obvious signs of usage. And here I see your point, where a visual assessment differs from an operational assessment. Especially on any high end locomotive with many features. For that matter, even a regular LionChief engine. If the sound or smoke doesn't work, it's not like new, even if it appears visually to be like new.
I don't know how a new grading system would work, especially on the modern stuff. Parts are far more limited today as well as quantities made. Here's a real advantage of almost anything pre-modern: Production runs were larger, therefore parts are more universal and accessible (meaning repairs are more practical).
Mechanical e-units certainly can have their quirks, but they are totally fixable. A circuit board is another story, unless you have a degree in electronics or just a lot of attained knowledge - as there are a few on this forum.
To me first and foremost, it's a matter of the seller being honest - which does not always happen. So then what to do? Next, it's become more necessary for the buyer to be knowledgeable of what they are buying, to do their homework, to be cautious and ask questions before making a purchase.
A scenario for honestly: If a high end locomotive, for example, has been repaired with lets say a replacement sound system or an improved smoke unit - which is better than when purchased new - it is now, by the current grading standards, no longer new or like new condition. Even though operationally, it could be vastly improved.
Regardless of any new grading system, today the weight is more on the consumer to be in the know of what they want to buy. If a seller cannot answer a question, doesn't know, or simply won't tell you - regardless of the vintage or features of the trains - the best idea would be to pass. As they say, buyer beware, which has become more true than ever.