The preparation, the sheer breadth of collusion -- word would get out before they could put the resources in place, and the moral Ethereum devs and nodes would ensure a quick abortion.
I'm not sure that the Ethereum devs would necessarily try to prevent something which might force Bitcoin to switch to PoS. And even if a majority of them will want to abort/revert an attack, doing so will undermine Ethereum's own purpose, since Ethereum has no agreed-upon obligation to save Bitcoin in case of an attack. So even though they could abort/revert a smart contract rewarding a Goldfinger attack
if a majority of the stakeholders also agree (otherwise the devs are powerless), unless they are required to do so by law, it would undermine the freedom of Ethereum.
I wasn't at all suggesting that devs would respond to prevent Bitcoin from switching. I was only saving devs would respond on moral conscience -- to simply attack another network using Ethereum resources (selling Ether as you said remember?) is not a coonscienable action.
Also, I personally think Ethereum undermined themselves long ago when they rolled back... mostly at the behest of the haves, but I suppose partially on a moralistic capitalist argument.
P.S. Reason I don't actually support or go against technical routes is simple -- I actually am very weak in technical discussions =)
P.P.S. I would actually really much like to see your theory put into practice to prove/disprove us all. Have a feeling we would see so many things happen in wildly different paths to what's been predicted. It would be fun, and we can dream, can we not?