Ethereum 2.0 has been proposed for quite some time now. If the temporary solution is to go for BCH block chain, then let it be at least, it will solve the problem of scalability that has been the complain of enthusiasts. All the same, if Vitalik brings it up and originally lunch it on ethereum blockchain then better.
Using BCH blockchain, will give more credence to BCH platform.
it might be good for BCH, but not for ethereum. ethereum users will begin to lose their trust. ethereum is a standalone platform, depending on other blockchain is not a good solution. scalability might be done if you use this method. but that doesn't eliminate the problem. blockchain ethereum must be updated immediately.