But the "viable product" bit is the hypothesis you're testing.

If you're saying "before you release it, it has to be believable as a product" - I think I basically agree with that, and for sure, that's a subset of the total things that might be "experiments" (because you can experiment with individual features, and stuff like that).

I suppose there are two ways of reading the word "viable", either "does this look sufficiently like a product?" or "is a product with this basic concept likely to thrive in the marketplace?". I think too many people focus on the former and not the latter.