I really respect and to a great deal, share your thoughts on keeping TSD a thing of tradition.
I do feel, however, that to a degree making up "forms" in one way can be beneficial. I've noticed that the downside of the same 4 forms that I know currently over and over again does have a dangerous disadvantage to watch out for. When you lock yourself into the same pattern, you lose your ability to be spontaneous, which can be a problem when your instructor makes you do drills involving random patterns of blocks, kicks, and strikes that you've never really done before. Despite my feeling that making up a form or so can have its benefits for an individual student, I definitely would not want to see TSD being warped by having "Master Joe Smith from Nowheresville, Kentucky's Form 17" be added to the standard TSD cirriculum, if you know what I mean.
ASIDE: From what I've seen, I get the feeling that alot of students these days don't really understand the full impact of the actual Hyungs- seeing them as just mere patterns of strikes and blocks put together to look really cool. If they were just that, then I'm pretty sure everyone would be learning Bassai Dai by the time they were at orange belt.