I think the way they pronounce Holo in the trailer is way closer to the japanese pronunciation than if they had used Horo. Sounds good imho and not at all like "hollow"
But even better, they kind of kept Holo's special way of talking. Not so "old" maybe, but at least she doesn't talk completely "normal"/colloquial.
Holo's voice sounds very nice also. Doesn't hurt the ears like so many others xD