My PC’s ancient at this point [2013], was interested with Geforce NOW with the official announcement with Battle.net support… But then it doesn’t support add-ons… interest flat lined right there.
“(Yet!)” isn’t reassuring… could be years before it happens, if at all.
With your gameplay being session based through Geforce Now it would make no sense for Nvidia to do this.
Each time your game session ends it reverts back to the standard game files iirc, that means that the ability to install addons needs to be within the client itself (not just a folder) and even if Blizzard did that (they won’t) you would have to reinstall and setup the addons on each gaming session.
Perhaps this little detail will finally motivate Blizzard to get some proper resources into making the UI actually work instead of very slowly changing it piecemeal to make it even more inconsistent than it already was.