I'm sure that Mindset Segment is Delta profiling us based on our history of past business and potential for future business to let CSAs know how they should handle us in present-day interactions. Frankly, it makes good business sense, they just generally don't want it to be transparent to the customers.
Looking at the relatively few data points we have so far, I'm making the following off-the-cuff guesses:
BH - Base Handling; non-status members, no special treatment
DW - Diverse Worldwide; medallions who have a varying portfolio of leisure and high-value longhaul travel
FL - Fare L; customers who fly a lot, but typically purchase non-refundable fares well in advance, not meeting the "SS" criteria
GT - Global Traveler; North American medallions who earns MQM primarily through intercontinental travel
IN - International; presumably, medallions with addresses outside North America
MM - Minimum Medallion; used rollover from past spending to make only FO, not high value customer
SS - Special Service; medallions identified as high value with high likelihood to bring considerable future business
Obviously this is complete nonsense since I'm making wild guesses at people's actual travel patterns, so I'm probably just as likely to be 100% wrong as even 20% right. So, folks who don't fit the above, this is where you start shooting holes in my theories!