[mrandish]

Based on the wording of your question, I can't see a way today to prove it never could, therefore the answer currently must be "Yes, it may someday be possible."

Note: This assumes that "conscious" as defined in this context is specific enough for the question to ever be meaningfully answered "Yes." This is a non-trivial assumption because there are criteria by which some would judge AIs as already conscious. Alternatively, some philosophers of mind have criteria by which they assert humans aren't conscious.