Heh, his and his father's names were taken from the names of constellations, Draco the Dragon and Scorpius the Scorpion. I guess it was a continuation of the Black family tradition of naming children after stars/constellations (Sirius, Regulus, Bellatrix, Andromeda...)
There are other constellation names I would've preferred to Scorpius. :o) On the other hand, with a name like Scorpius, the gryffindor kids can tease him.."Nanner, Nanner, Scorpius, the Porpious" or maybe, "Scorpius, the dorkius" if they want, too. Yes, I know it's spelled Porpoise..
Ah, but as a personal reminder of Voldemort and the Dark Side, Malfoy had to be a dragon.
Rowling had strongly hinted that knowing the Bible would tell you how it would end, and there's one place only in the New Testament where dragons are mentioned.
Look at Revelation 12 and subsequent. If you want the plot of Book 7, there it is....