Hi and thank you, for your very nice answer!
It infact is nothing new.- You were always able to play games from VP using SteamVR and I like the Idea of officially labeling those games that work with a WMR supported tag, but it is kind of fishy to make users of one launcher install an competitioners launcher to make games on their platform work.
Another thing is, it is a bad start, since you have around 600 titles on Viveport and there are around 90 that are marked as "working with wmr". Eaven some of your best games that support WMR are not marked as wmr supported games. (yet) This is a bad start, since interested people will check out the store and won't do that on a daily basis to see if new games are now marked as WMR.