Any chance I'll get lucky on next week's BA 294 and get the new F class suites? How often are the newer planes subbing in?
On the ORD route right now - zero chance. Only 6 of the 16 B77Ws have the new F suite, and ORD is not a route they are serving. A last minute substitute is also very unlikely because if your flight is selling F as an old B777-300ER aircraft, that will be sold as a 14F cabin flight, so unless loads were light an upgrade to the new F suite on a busy flight would immediately mean a downgrade for up to 6 pax.