I don't have a problem with number one, 40K is expensive, so it can take a long time between when you decide to start playing a new army and when you finish it. I think the game as a whole is more fun when every player can try out the new codex or whatever, rather then just one faction being excited about it. I do see how it could be abused heavily by a powergamer though.
On a related note, what about a different version of type 1 where the models are still from the same army? Ie. "these unconverted ork boys 'count as' tankbustas"?