There are two separate questions here:
Earning - does this have a net effect on how points are earned? This seems likely - HVCs will earn more and lower fares will earn less. I predict this drives some lower tier elites away similar to how loss of E+ has driven some UA flyers away but will ultimately prove to attract some higher yielding fares. I don't think the net effect here is significant due to competitive situation.
Redemption - the big potential change is if redemption is impacted. In this case some HVCs that book J travel to Europe or Japan will hate this change and switch very fast to star or one world. It sounds as though this may not be included in first phase but to me this is big potential change as this was the only way you could reliably get a better than 1-2 cent return on miles to places I like to travel to. Having said that, the decreased availability of low J awards in recent years has nearly driven me away so I expect some will stick with DL even in this scenario. I doubt domestic redeemers will be significantly impacted even if they go this route.