GW scrapped all codexes for 40k between 2nd and 3rd editions, they basically started again from the ground up and re-wrote the game. People were quite forgiving, even those of us who did buy all those books. This was also done in fantasy a few times too, 3rd -> 4th editions was a big change and basically thats when the "Codex" army book system they still use was invented. After a time they did the same thing again for Fantasy, 5th -> 6th editions, all army books were scrapped. Now the changes to the game between 5th to 6th werent a total re-write like 40k had, more tidying up and just re doing the magic phase.

It may be a little early, but I suggest that 6th edition 40k does the same thing. I really appreciate the new 5th edition rules, I think they are a huge improvement in all the little tweaks that were made. But I think GW could do much better if they scrapped all the codexes and started over.

Warhammer will, in my oppinion, never need this again. the game is pretty much finished and they could concentrate on army books then whole new armies maybe?
But I think that 40k isn't quite as finished as Warhammer. By invalidating all the codexes and releasing 40k as a new fresh start they could fix all those little issues they haven't been able to change due to the codexes all having them in.
3rd ed was a hugely improved game from 2nd edition, if they could improve 5th -> 6th even half as much I think we'll thank them for it and have a much improved game that, like warhammer, would never need re-booting again.

I'd love to see what you all think but please don't post specific problems. I've tried to avoid them here since any that are posted are guaranteed to drag the thread off topic.

So what would say to scrapping all the codexes?