Actually that somewhat leads to another questions - out of TK, SQ, TQ - and BR - are any of them likely to sell/do bidding upgrades?

If I buy the cheapest Y ticket on IB and there is space, I can usually buy an upgrade to J for $535 on the MIA-MAD segment - so if expert flyer tells me there is enough space - I might buy Y and almost count on getting a cheap paid upgrade. American MUC-CLT - pretty much always available for $595 even from basic eco etc.