As I read your proposal I kept fluctuating between thinking "that's a great idea" and "people should check out as many different keywords in their search as possible anyway; this isn't the search engine's job". Since the purpose of most searches is to answer a question that you lack knowledge on, it's not unreasonable to suppose that you might not know / think of all of the keywords that might turn up the answer to your question, so your suggestion definitely does have merit.
As to exactly what form this should take, I'd question whether anything more complex than a "smart synonym" type search / recommendation system would be worth the trouble. Even having the search mention that "related keywords to try would be..." would seem to settle into a fairly comfortable place when considering the law of diminishing returns. I think that implementing some of the changes mentioned on this node
and adding this "smart synonym" feature to the existing search facilities would provide the best return for the time investment.
But then again, what do I know?