I would really call these changes minor. It’s even just a soft fork if block rewards would not be touched. If the code for the Beacon chain is finished, then it’s just modifying the fork choice rules.
Good question.
If there is much less money to be made from mining, then also, in general, the market demand for newer chips is lower. Hence, it will be less profitable to develop new and more efficient hardware. But it’s hard to say, whether it will be still profitable enough for people to develop specialized chips.
I think the main benefit of switching to POS is the increased security for the Ethereum 1.0 chain. Look at the charts, the hash rate has already halved itself: here. And at the latest with the next hard fork, there is plenty of cheap hardware available. This decreased the theoretical-attack costs for POW chains.
With POS, we could increase the theoretical attack costs again.