That's pretty much what they're doing, except Legion's goes to Azsuna and MoP's goes to your faction's town in Jade Forest.
This of course makes no sense. Dalaran is currently in Broken Isles so it's a portal in time too. The Northrend portal should go to the Dragon Shrine and the Legion one to Legion Dalaran, but everybody has a Legion Dalaran hearthstone so time-travel or not I'm cool with it.
The MoP portals to Jade Forest are just plain stupid. Unnecessary inconvenience. Just phase them to portal to MoP shrines at level 90 and it would work fine.
Also the portals to Caverns of Time, Karazhan, and Dalaran Crater (Hillsbrad) are being removed entirely. They were all useful and are now gone forever.