Here are MCP locations as of March 2021, sorted geographically. The MCP started in 2012-13 with a few well known independent destination resorts (Aspen/Snowmass, JH, Alta, Squaw/Alpine). Most are also on Ikon.
The MCP continues to be worth considering for people who can't take ski trips that include 4+ days of skiing. Especially if it's possible to take more than one trip making use of the MCP at more than one location.
•Mammoth Mountain, CA - Ikon unlimited/5, MCP, Alterra
•??/Alpine, CA - Ikon unlimited/unlimited with blackouts, MCP, Alterra
•Big Sky, MT - Ikon 7/5, MCP, Boyne
•Jackson Hole, WY - Ikon 7/5, MCP; $150 add-on to Ikon Base
•Grand Targhee, WY - MCP (new for 2020-21)
•Alta Ski Area, UT - Ikon 7/5 combined Alta/Snowbird, MCP (separate)
•Snowbird, UT - Ikon 7/5 combined Alta/Snowbird, MCP (separate), connection to Powdr
•Aspen/Snowmass, CO - Ikon 7/5 combined, MCP; $150 add-on to Ikon Base
•Arapahoe Basin, CO - Ikon 7/5, MCP
•Taos Ski Valley, NM - Ikon 7/5, MCP
•Sugarbush, VT - Ikon 7/5, MCP
•Sugarloaf, ME - Ikon 7/5, MCP, Boyne