Yep, it has eight limbs. I think by now you should have checked it out but I will leave a picture depicting them anyway.
You can see that it has 4 smaller limbs on it's back.
Here you can notice up to seven you can see it's noticably bigger frontal limbs and can see up to three of it's posterior limbs which are notably smaller.
Hmmm... I think they should do a minimum of 15 megas in OR/AS and a maximum of 30 megas. I think it would be interesting to see the Johto starters get megas since they are a reward in emerald for compliting the pokedex. But really I don't know. They should concentrate on gen 3 and 2 megas. If we don't get some expected Megas we still have X and Y's sequal. So we can expect some to be there. However I think they should do gen 4, 5 and 6 in the upcoming third version. Megas that should atleast be in OR/AS are mega Seviper and mega Zangoose and I think that Solrock and Lunatone, Salamance, Flygon, Camerupt, Sharpedo, uuu, imagine a mega Wailord now it's size would be scary. Reli.. well no, maybe if primal regression extends beyond the weather trio it should have it. Shiftry I guess and Ludicolo well... Idk. Plusle and Minum were trade marked right? I guess it's a possibility we get those. Nintendo surprise me and make a mega Raticate in Hoenn where of all regions it's so pertinent.