Increasing the blocksize makes every ~10 minute block twice it’s current size. Seeing as SegWit already doubled the bandwidth requirements for a full node by doubling the transaction throughput, 2X would effectively quadruple it. There’s a lot of data to which I can’t currently source that show how this effects the ability to run a node. Not only is it an issue of storage, bandwidth caps in many countries are the much bigger issue, which is highlighted in the screenshot of the Ethereum Reddit thread that none of the developers replied to. Easy to overlook for many when they are sitting on their computer chair in air-conditioning.
My only guess as to why they didn’t add replay protection is because of this: Bitcoin Cash had replay protection, which self fulfilled it being called an alt-coin. With the community rejection of of 2X, the result will be similar: It was an attack, so it’s an alt-coin. Both forks in turn may wind up being the best thing for Bitcoin moving forward.