I think you're right. There might also be a weight problem. You want the key to pop back up rapidly. Don't know if the spring in regular switches would be able to deal with it. If they would, they would be needlessly hard to push down.
There's a lot of plastic in SA keysets, especially sculptured SA. To me they seem to work best on heavier switches, like blacks (as I'm using now), greens or clears.
I guess if the springs in the switches are strong enough you could have keycaps made from lead!
Except for the poisonous side-effeects of lead, of course.
And the fact that it is sufficient soft that the keycaps would deform over a fairly short period of time.
And they wouldn't look very nice either.
Ok, scrub that, lead keycaps is a BAD idea
