You'll then have 10 very rich people basically in charge of bitcoin. I'm sure these now powerful and influential people will have meetings and discuss various ways to control bitcoin. The rest of us will be pawns in their game. It would be very easy for this group to come to a consensus and control bitcoin to their whims.
I doubt whether they will do anything like that. If they do so, then it will harm the reputation of the Bitcoin, and the exchange rate will tumble to near-zero. In the end, it will affect these powerful mining cabals also. But I agree with you, it is theoretically possible to do so. One of the fundamental flaws of Bitcoin. But as of now, we don't have to fear about it.
If this happens, would developers develope changes to bitcoin so to block big farmers?
If not tools to avoid big theft of bitcoins is going to happen, is there also a resistanse towards developing a other mining strategy for bitcoin?