US airports I can think of with DL international flights that I can think of that have accessible lounges for GM+ that won't be able to use the Sky Club:
BOS (Virgin Atlantic, Air France)
JFK (Virgin Atlantic)
LAX (Korean Air)
The JFK clubhouse especially might get crowded.
Would not be surprised to see more carve-outs added to the VS Clubhouses (also would not be surprised to see the JFK Clubhouse merged into the new D1 lounge with the existing Clubhouse re-branded as a straight Plaza Premium lounge).
It also seems likely that many elite holdouts with frequent international economy travel will finally break down and acquire the Reserve or Platinum card. Also see a chance this benefit returns as elite ranks are thinned out, assuming DL successfully resolves the broader overcrowding issue, given it's such a deviation from SkyTeam policy.