Resonance of carbonyl
Yes, resonance should never stop at the most likely resonance structure. If you’re really willing to play the game, you can take it even further and consider singlet diradical structures where the bond has been broken into a spin up and a spin down electron, each one of which resides in a different orbital. And more, and more.

(Side note: this is why it is useless to ‘count’ resonance structures. The only correct answer to ‘How many resonance structures does $\ce{X}$ have?’ is ‘Always one more.’.)