I'm all for voice acting in cutscenes, but keep in mind that the dialogue is always being tweaked/fixed (sometimes right up until launch of a patch).
The addition of voice acted lines for ALL dialogue would increase development times, costs, etc. Costs we can mitigate in some way, be it a more costlier sub, etc. But development times are not an easy thing mitigate. MMO's that are multi-lingual, take a fair amount of time per development cycle, especially if they are doing simultaneously releases in each language, which is how SE does things with XIV.

Realistically, I think its best not to implement VA for all dialogue. I dont want to wait 6months to a year per patch for the same amount of content we normally see....