I think this would be bad for toy collectors and parents as Hasbro and Mattel keep each other in check with their "competition". I can't think of another player in the toy market big enough to take on a combined Hasbro-Mattel company - certainly not in action figures or dolls. A merger would basically see HasMat coming up with their own price points and laughing all the way to the bank once they'd paid for the merger. Lego is a dominant player but really only exists in one section of the toy market and certainly not Action Figures, nor do I think they have the desire to go beyond their Lego based characters and franchises at the moment.

If Takara Tomy was allowed openly into the global Western markets beyond Asia in a real way that might lessen some of the profiteering that could go on, but as Hasbro and Tak-Tomy seem to have virtually the same franchising licenses I can't see that ever happening unfortunately.

eg. In the Hk market Tak-Tomy die cast cars ensure Hot Wheels and Matchbox have to keep their prices lower just to be able to compete.