I too got a great offer in F and onward to BKK,again in F, for the same price as J. Currently there are only two seats taken-me and Mrs SS.
The 3rd daily 3 class has only just started and runs until 31st December when it goes to a 2 class - all are 777-300ER. There has been no substitution yet-I think it unlikely, the following explanation may help.
Local PPRuNe "experts" state that it was never the intention to have a permanent 3 class schedule but lack of spare 2 class metal, and the desire to make BHX 3 times daily soonest, necessitated its introduction. And no-an A380 2 class was not on the cards because EK has a most useful cargo income out of Birmingham ,maximising it with the 777.
EK had 42697 BHX pax in May and 38567 in June, a traditional quiet month.
SS
Incidentally, I have nabbed F seats ( without the service) from J,twice in 18 months when a 3 class was substituted