Preamble to longer answer
As several other commentators and answers have noted, there are aspects of consciousness (immediacy, time-based, self-identity, action/agency) that suggest that consciousness has incompatible properties with abstractions, such that abstraction/consciousness identity seems extremely implausible.
This is also the case for consciousness and material, and these strong differences are why materialist identity theories are also intuitively rejected by property dualists.
These intuitively identified differences become a rationale to adopt a "substance triplism" model of our universe, as Frege and Popper did.
An intuitive problem for dualism, or triplism, however, is our further intuition that fundamentally different things cannot interact.
Yet our world seems to have regular interaction between these sorts of radically different things -- abstractions are embedded in physics, and our mental reasoning, consciousness is key to what we do and why, etc.
So any dualism or triplism that accepts the interactive causation we observe, must admit that these three types of things share enough "essence" to be interactive, and the absolutist non-interaction of our intuition is wrong. This possibility has been strongly reinforced by the very non-intuitive features of modern physics (QM and GR). Our intuitions, forged in dealing with medium-scale life as hunter-gatherer animals, are not a valid guide to the more fundametnal nature of our universe.
Accepting this opens up the logic space of possibilities, such that all of materialist property dualism (matter has both material and consciousness properties, that it exhibits in parallel), materialist emergence of consciousness, materialist identity theory, mental idealist emergence of consciousness, mental idealist identity theory, and abstraction emergence followed by abstract identity theory would then all be POSSIBLE. And then we would need to examine how well they match the world to see if the supporting evidence for them is strong enough to overturn our intuitions.
The last, that functions are emergent from brain processing, then functionalism develops either dual properties, or is identical to consciousness, is basically what functionalism and its descendant ideas discussed below proposes. So now on to:
Longer Answer