Now since we agree to the fact the home miners will dominate at certain point, how reliable will bitcoin be then when 1 large farm can switch their gears back on and easily attack the network or force new rules / hardfork or whatever shit anyone would do? The blockchain size by then will also be very large,nodes number might as well drop significantly , making every kind of attack much more easier than it is now.
Probably not as easy as it sounds. You are still going to need the gear and the power. No big miner is going to just shut down and go away. They are going to sell the buildings / get out of the leases they are in and sell off the gear. Sitting on the gear to attack later is just not good business. Newer, gear more efficient will still come out since there will be a profit in designing and building miners so even if they kept it they might be behind the curve .
The biggest issue would be a pool or group of pools that gains enough hash. But I would think the same backlash that hit ghash.io back in the day would happen again.
And as Phil said it's probably not going to happen for at least 10 years so there could be some other changes in mining that we are not even thinking about.
Edit: As for the blockchain size, I really think that is a non issue. I just got a 1TB SSD for under $100 at Amazon. I could have gotten it for less but I was in a hurry and just wanted to get it ordered, did not want to stop and shop to save $10.00.
-Dave