If you must fly A380 in F, then fly Emirates.
If you chose TG, then no guarrantees you will get the flight in an A380 F in January next year.
"Getting Tg'd" is part and parcel of flying on Thai.
(Unless, of course, you are on "protected routes" such as HND and SYD,
where the Thai VVVIPs would dare not fly in business, and TG would consequently dare not swap out for an aircraft without F - someone would get fired! )