I’d speculate the lounge access policy will be- no D1 Lounge access, and SkyClub access only if you have other qualifying credentials (so in addition to STE+, qualifying credit card access or membership).
Seat selection for elites will be far less punitive than UA and LH’s versions.
I agree: D1 Basic won't prevent SkyClub access the way BE does (which was what I was going for). D1 lounge being a major difference for Classic, though, might mean that DL holds off on US-origin Basic D1 until DTW and ATL get D1 lounges (or maybe the fare rules for US-origin only offer Basic if going through JFK/BOS/SEA/LAX... in which case the existence of D1 Basic in this forum will go from "affront to humanity" to "another case of DL hating its core hub captives")