>>17644904>>17645007People try to sweep the evidence under the carpet, but - given how GF plays with their designs - this screencap makes a lot of sense.
GF has already stated that they create most of the pokemon in large pools of designs so that they can be distributed to make as much as possible from their potential.
These megas were likely made around the same time as the ones that were released so far - but were most likely held off due to being sub-par design wise. People have wondered why there are some Megas in the XY for pokemon with small fanbases. The most likely explaination was that their design was still better than the popular ones with the designs in the OP. GF most likely didn't wanted to spoil their grand entrance of XY - so they shelved these.
I suppose that these will come in the patch after XY's sales peak - the customer base will already have the game, so releasing those poorer designs will not hurt the business of the company.
Convoluted, but entirely feasible and very likely.
