I have a feeling if the do a Decepticon Masterpiece figure, it'll be Starscream.
If they did a megatron, it's really a tough call on Takara's part. You have to consider this...
"Ok, let's make a MP Megatron!"
"Ok, but should we scale it so that his bot mode is the same as Optimus or so that his gun mode is the size of a real gun?"
"Is it wise to make him a gun again? I know! Let's make him his second form! A tank!"
"But then we'll alienate the hardcore fans!"
COntinue from there.
Starscream is almost as popular as Megs, has less contriversy over his alt mode, and Hasbro could also fully support the production of it.
(And no "Hasbro SUX!!! They can't make guns or long pointy smoke stacks!!!!" It's not their fault, they're following US laws and I salute them for that!)