It sounds like BA Gold would be reachable; I confess I'm not familiar enough with QR's program to comment knowledgeably. But let me ask - what Emerald perks would be important to you compared to your baseline Sapphire ones that you'll get as LT Plat anyway? First class lounges?

Obviously Sapphire or higher with another OW airline would get you into Admirals Clubs on domestic itineraries (or FLs if you get to Emerald) but is that key? For me, when I was EXP the biggest perk was the EXP desk itself, with the SWUs a distant second. I had very bad luck with auto upgrades on domestic flights - SEA was too small an AA market, with too few destinations, to bank on A space being available - they just never released it, and I really got tired of playing roulette on C seats opening on overseas segments from AA-accessible hubs for TATL or TPAC flights.

So for me the EXP desk was really the main perk, rather than the SWUs or auto-upgrades. YMMV.

BA's award system sucks for US flyers IMO due to having to pay for multiple awards on simple connecting itineraries, and I believe BA has dropped the "cheap" Avios tier for shorthaul flights in the US. Not to mention having to pay "first class" Avios for domestic F simply because AA doesn't have J on most sectors. And also, of course, there's the matter of the dreaded BA fuel fines, regardless of what BA calls them.

So I'd evaluate what I'd use BA status for - MFUs from WT+ to Club on TATL trips? 2-4-1s?

And then - out of the box - I'd look at Alaska. Decent redemption rates, increasing reciprocity with AA, LOTS of excellent earn/burn partners including the likes of Hainan and Emirates, and once they've swallowed Virgin America they'll (hopefully) retain VX's airbuses with their fabulous first class product. Just sayin' - have a look at AS.