I believe I read somewhere that if you get the digital version you do actually choose in-game, afterwards it locks you into one path permanently until you buy the other version. The demo version showed a second page of save files so I assume once you download the second path the choice shouldn't be locked in anymore, but I'm just guessing for that. I don't see why the choice would be locked if you own both sides.
Considering each path has 28 levels, with at least 6 shared, I don't mind paying a discounted price for the other side.
I'll be getting the Nohr physical version but I think I'll download the Hoshido side (and eventually the third path if it isn't available at release) early on in case I end up liking the Hoshido characters more and don't want to do Nohr first. As of now I'm confident I'll play Nohr first though.
Removing weapon durability is a change I welcome and it'll take some time to learn the new weapon triangle. At first the two sides thing bothered me but the more I hear about them (exclusive characters, possibly 22 different levels, no grinding vs grinding, win condition difficulty difference, different classes) the more the idea that they are going to be two fairly different experiences sinks in.