To be honest, I've never understood the 4pm entry for party ticket holders. Sure, it's a great perk, and I'm assuming it was likely done initially so that security and entry CMs aren't slammed with party goers right at 7pm. But I think over the years with the 4pm thing becoming pretty much common knowledge, all they've done is moved the problem up to 4pm instead of 7pm.
This doesn't impact me personally because I have park hoppers and at another park the morning of
MNSSHP anyway, so I can get into MK whenever, but I can see how this could put a damper on things for people who buy one less day on their park ticket and use only MNSSHP for that day. It'll be interesting to see how it pans out and will be interested to hear reports from the first party.