Upon activation of The SegWit Omnibus Changeset, previously fully-validating nodes are rendered non-validating nodes, as they are incapable of validating SegWit transactions.
Upon activation of the Classic hardfork, around 25% of nodes on the network--probably more since the activation threshold only counts miners and plenty of people seem fond of running old node versions--would be either forced to upgrade or kicked off the network entirely... unless the user ecosystem (vendors, exchanges, etc...) isn't supporting Classic anyways so 75% of miners just end up forking themselves onto something no one uses
Agreed. I'm just trying to cut through the FUD that claims The SegWit Omnibus Changeset has no effect upon legacy nodes. For such is a lie.