So many people say this with every rule change DL makes. Reality is that few really follow through on it. I sincerely hope you do, but if you do, realize you will be the exception not the rule. Most frequent flyers book an airline based on convenience (hub captive, better connections, etc). So changing airlines just due to one rule change is very uncommon.
Maybe, maybe not. At some point, Delta will have watered down the benefits of status to the point that people that often pay more to stay on Delta's flights will instead mix in significant numbers of flights with other carriers. If a large group of travelers starts flying only 65% of the time with Delta instead of over 90%, it's going to hurt Delta's bottom line. I'm not offended by any of Delta's changes, but I question whether they have gone too far and caused unintended negative consequences for the airline.