I would not be a part of any organization where an engineer decided if I was a designer or not. Since non designers could not be in the organization, it makes no sense that they would decide who could be.
Generally though I think the rest of what YO describes could be achieved by a sufficiently motivated local chapter.
funding/membership dues are going to be the biggest hurdle. YO, how would you charge?
I work with motivated local people to do IDSA stuff. There are the local (and regional) students, a few designers, and us/ the board who are motivated. Everybody else seems to be lethargic and disinterested, but that is a staple of the area I live in. I think if you are in a city that is generally optimistic your local chapter can really do cool things and have a good turn out for everything, Chicago comes to mind.
Funding and bookkeeping are always a hassle. I would think that there is some firm somewhere that dose that sort of thing. Then since it would mostly be online with maybe a regional or national conference every year, it wouldn't be all that hard. Building additional value for membership would be the hard part.