The lack of replay protection is a huge problem as well, I don't think there is a way to safely transact your coins only on one chain. It would be a race in the best case scenario and one chain will almost always win and put the coins in danger on the other chain.

The just means that the it is unlikely that these chains will coexist. As they won't be able to safely so a compromise might be necessary.
This puts everything on bigger stakes as well. I think this could be a very big deal. It is basically miners vs developers. And users might be on the Core side, but no one can be sure. So anything ca happen.