How exciting, I get to be the pedant: it’s “stream-of-consciousness,” not “stream-of-conscious.” Conscious is an adjective; there can’t be a stream of it.
I see your pedantry, and raise it one more!
Through substantivization one can definitely have stream-of-<adjective>. Think "a stream of blue" or "a stream of the poor".
People often shave off the tail of well-known expressions:
“same difference” → “same diff”
“no big deal” → “no big”
“It’s no big.”
“fair enough” → “fair”
“Fair.”
“good enough” → “good enough” → “good”
“Yeah, that’s good.” (implies good enough)
“I don’t know” → “dunno”
This is how British people feel every time we read "full-featured".
I think the same when I see "your subconscious". No, it should be "your subconsciousness"
On the other hand English is highly imbued with lake of morphological inflection and other explicit lexicalization by grammatical type. So this is really just following the main stream tendency.