First of all, sorry for bumping an old topic, but I've always wondered the same thing about this awesome franchise. If I could somehow purchase the game rights and fund a new entry in the series, here's what I would do:
It would be an RPG. It would stay 100% committed to the source material, universe and tone. The story would pick up from where Zwei left off, with Jean-Luc Lundi wandering through a desert, dazed and confused, mumbling about his friend, whom he must find. He's found unconcious by a merchant and his daughter who take him in, and then their village is attacked by the empire and things escalate from there. The whole game would trace Lundi's evolution into the Sky Rider, whom we saw in the intro of the first game.
And probably the most crazy idea of mine?
I wouldn't call it Panzer Dragoon. I wouldn't even pertain to any connection with the Panzer Dragoon series whilst showing it at conferences such as E3 etc. I would simply release it with everyone thinking it's a new IP. Only when people have completed the game would they find out it's linked to the original series and as a reward (Pandora's Box style, of course), they would unlock completely remastered versions of the four original titles. Obviously publications would report on this and the surprise would be spoiled, but I think it would be viewed as an artistic masterstroke.
Just my thoughts. Feel free to shoot me down in flames.