I guess I disagree on this point. One of the only drastic changes I could see being made that would result in the system still being "40K" would be diversion from the typical IGOUGO. Doing so would obviously open up lots of strategic possibilities.
If they changed the game from a large battle game to more of a skirmish game, it would not be 40k. That's a drastic change. If they went a more "warmachine" route and had fixed units, with unit cards, abilities, that would be a drastic change that would make it quite "un-40k."
I personally think your comparision to BattleTech is really disheartening. I don't want anything near that amout of paperwork involved in 40k. It works with BattleTech because of the number of models; it would be a nightmare with a larger format game.
You seem to want a complete rules overhaul, and I don't know the system even needs that. I don't know if people consider TLOS to have been a major rule change. I don't. The problem with all of the rules changes will be addressing the inherent rules loophole search that goes on with the game, and the subsequent FAQing. My group isn't that hardcore with the rules, so those types of things have never been an issue.