I think those fare classes are "tongue in cheek" and likely they should be "whY S,P,E,K,U,L,A,T,I,O,N?"
Firstly, YSBMHQLVKGTRXW, is incomplete. It is missing Z & N, refundable (and eligible) & dynamic Main cabin awards respectively. As of now, Main Cabin Fares, Saver & awards are
YS(MVP eligible) 50% COS*
BM(MVPG, eligible) 25% COS*
H(MVPG75K, eligible)*
QLVK(GGU eligible, status not needed)
GTR(Discount Main, ineligible)
Z (Refundable, eligible award)
N (dynamic, ineligible award)
W(Saver, ineligible award)
* Eligible fares provide for an immediate complimentary upgrade into the F cabin if U (upgrade) space is available. All fare classes listed above an Elite Tier are also eligible for that Tier.
AA is YMLKHVGNSQ for AS EQM earnings, BE, fare class B on AA don't earn on AS. T is used for Main Cabin awards. S is most often the fare basis that AA offers Y-UP into PE(P) or F(I)/J(I) in domestic/international F/J.
AA uses R for discounted first/business while CX uses R for PE and although not oneworld, so does SQ. AS might very well reassign a new fare class to replace discounted non Saver Main fares. That could leave R for a future "unbundled" J cabin fare that perhaps doesn't earn a COS bonus or grant AL access.
If we want to speculate further, I can see the top 2 Y fare classes dropping to a 25% COS with no other COS bonuses below that. AS may also drop EQM to 50% on Saver X fares or if they match AA you can use all your benefits including upgrades but the X fare will earn zero EQM. Maybe RDM and/or Elite Status bonus only?
There might be provisions added also for a lower Main Cabin Fare class that will be eligible for MVPG100K too, although that could be added later in the year.
Lots of speculation. I will wait for the concrete to set!
James