Seems like you were being facetious, but “Caps Lock” and “Compose” are two different functions. You seem to like to map the “Compose” function to the key that by default is for “Caps Lock”. It would be as stupid for the key to be labeled “Compose” when it does the “Caps Lock” function, or for the key to be labeled “A” when it actually produces “X”.
Personally, on my current laptop Fn+K is a hidden scroll lock, but I have it remapped to “Kompose”. 
(And I can type Fn+K Fn+K : D to get “”.)
That was said in a comment in the discussion of the Keyboard blog post.
My impression is that it’s still possible, but you risk breaking things because the individual keys weren’t designed for being removed and put back on. And I’d guess Framework doesn’t intend to sell individual key caps. But who knows, maybe someone will in the marketplace?