Interesting. I was also familiar with the other theories but hadn't heard this one. I think it's plausible: Melchizedek may have been one of the "sons of God" referenced from time to time in the scriptures.

It's possible Melchizedek was a foreshadowing of what Christians will be on the renewed Earth: priests and kings in authority, ruling as God's vice-regents, which may actually be what God intended for humans all along, but sin led us astray.