About in 2 weeks on 2nd of June when MoP prepatch hit realms.
It will not work on pandaren of any class (including pandaren monks). Other classes and monks of any other races (everyone except goblins and worgens, because in MoP they couldn’t become monks) can use the boost.
This is, however the subject to change as MoP beta is changing every few days right now. Youtubers say Blizzard may overthink about restrictions to Pandaren boosting.
This seems to have changed. now on the 85 boost its says this…
Level 85 Character Boost only available on WoW® Classic progression realms (currently Cataclysm Classic™). Boost is only usable on the WoW® game account for which it was purchased or redeemed as a gift.
Level 85 Character Boost (Progression) also usable on Pandaren race and Monk class characters (available with the release of Mists of Pandaria™ Classic Pre-Expansion Content Update, planned July 2025).
Not available in World of Warcraft® Classic Era
Character Boost cannot be redeemed on “Fresh Start” realms
Requires World of Warcraft® Subscription or Game Time