In the Lion video, the player holds the banner rather than it being attached to the mount (think Argent Tournament jousting mounts and the way you hold your lance). I assume it will be exactly the same for the Scorpion.

Sit on the Scorpion? Nah. I'd want my toon to be standing on it, gripping spiked chains attached to its pincers to control direction.

My thoughts exactly, it doesn't really look like they've thought out how to sit on that thing. all of the larger races will look like they're getting stinger'd in the back all the time, especially taurens. + a saddle will look semi ridiculous.... however it might work if they position riders right up against the tail and have a long bridle attached to those really tall mandibles it has, that would actually look pretty decent.

As for the Lion, it looks good, its something I've always wanted as a mount(mountjunky) but the mask thingy its wearing makes it look odd. Tabard "barding" is nice but it makes the flag piece completely unnecessary. I'd be happy with both, without flag, and so long as I'm not getting "murdered" everytime I ride my scorpion :P