The rumour states that the masterpiece following MP-44 will be none other than a new version of Bumblebee, with a robot mode closely resembling the G1 animation model and with an Alt mode to match the chibifed cartoon model which was done to match the original G1 toy.
The rumour also gives a run down on what he'll include and a Japanese price as well as his release date. These details are included in the original and subsequent posts. He also states that preorders will open on the twelfth of February. Apparently included is the figure itself, a Spike figure, two different faces, a gun effect part, a numberplate, seal and instructions.
Prehaps as proof to these claims, or as a reaction to the rumour, the TagHobby website created a listing for the figure, with matching details.
Here is what the listing says:
[BREAK NEWS]
TAKARATOMY?2019?9??????? MASTER PIECE?? MP45 ??? Ver.2?????????Figure????Effect????????13,000(???)??????????????????
TAGHOBBY get the updated news!! TAKARATOMY will release the TRANSFORMERS Master Piece Series MP45 Blublebee Ver.2.0 in Sep 2019. It include figure, weapon and effect part. We are very surprise for the price of ver.2.0 is 13,000Yen(Not included tax).
No source is given on the TagHobby site.
So again, it must be stressed that this is all rumours currently.
Till then why not have a look at Seibertron's own gallery of MP-21 Bumblebee to see the old version or check out a top 5 list of non-movie Bumblebee toys as compiled by several Seibertron.com users:

Transformers Masterpiece Bumblebee Gallery
Top Five Non-Movie Bumblebee Toys
What do you think of this? Would you pick up a new Bumblebee? Let us know in the Energon Pub and stay tuned to Seibertron for all the latest news and reviews!
