But we have to beware of AI or it might become self aware, realize humans are a disease and go all terminator on us..
In all reality the overheads on a proper AI system for a game like an MMO would probably be huge and not worth the effort..
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The main issue with a VR MMO or anything VR is the nausea factor, some people complain about some games on a standard computer monitor giving them nausea.. Having a VR headset on the nausea factor would increase very fast..