I don't think futures necessarily "suppress" prices; I think it just makes the markets a lot more sort of "dramatic" than it should be.
And no, I don't think ETF will be "the nail in the coffin". Though it will definitely help A LOT with market liquidity. It will be significantly harder to move the price to either direction if enough money comes in.
I believe it is possible that an army of short-sellers can suppress the price, and probably also crash it. BUT it also goes to the other direction too. Short-sellers can also be short-squeezed once an army buyers, spot or futures, start to buy.
OP, do actually believe short-sellers will, or can, short and suppress Bitcoin forever?

Unsure, hence the question. I do know the banksters are ruthless and they've done it before with silver which has been suppressed for many decades (and still is). But silvers paper market is many multiples the nonpaper market (more than 100x). If bitcoins futures market gets bigger relative to spot market, then perhaps it could suffer the same fate. Hoping it doesn't get to that stage though.