It should not be forgotten that almost the exclusive user of lower airspace outside of controlled airspace is GA. The majority of GA operates at speeds of less than 140 knots.
These aircraft are the users and their needs paramount. If NOTAMS fail to communicate the information needed by these users then the system has failed.
As is quite evident from this thread, referring to a DA20 does not leave the matter free from interpretation but in fact causes confusion. Whether or not it should, is academic - face up to reality - how many GA users know or care what a DA20 is - what they want to know is what it is doing, how fast it is going and whether it is able to manouever.
It is extraordinary (and in reality not the case) that users can inject whatever they like into the system. Were this so, and using the same logic, every time I particate an aeros, I would post a NOTAM to ensure I had a "protected" area in which to operate.
No, as I have said previosuly NATS have a duty of care to their "customers" to provide them with the information THEY require to enable the safe conduct of flight. They are patently failing to meet that duty of care. No amount of tinkering with the presentation of their web site will change such an unsatisfactory state of affairs.