I actually think Epona will be our companion this time around. Not in the traditional sense (she won't talk and will follow us only where she is able) but we've seen how much crap Epona is lugging around for us this time (bags, sleeping bags, weapons ..) so I imagine she'll be sticking by our side a lot more than we've been used to.I actually don't think there will be a "partner" this time around.
Seems like she will be our sort of 'caravan', a movable home for Link during the adventure, a vehicle on which we can store stuff.
Plus it feels like they are making a point with this one to make us feel more connected to the natural environment of Hyrule (or wherever this is), what with all the wildlife; birds, goats, wild horses etc. So a less intrusive companion in the form of the horse would be perfect to emphasise this.