They could go with two different routes with Warfronts :
1/ Focus on the "Open-World Warfront" side, essentially remastering what the Ahn'Qiraj war effort was in classic with pvp objectives.
Some feature / phase example :
=> Make people choose a faction (example: Desolace War front, either join Magram or Gelkis or Kolkar or Galak or Maraudine) and gather ressources through the days to improve your base
=> An assault / expedition phase, where factions would fight each other to win some locations, magical artifacts, or recruit neutral forces, in the zone. (Mixing some PvP and PvE adventures).
You could imagine a system where factions could ally to prevent unbalace (in case for example the Magram faction has too much players or ressources, other factions could ally)
=> A final "Epic War" phase, where factions could unleashed all ressources/magical artifacts/etc they gathered against each other, and factions could siege each others base.
2 / Focus on the "Instanced Warfront" side, nearly the same as actual Warfront, but harder and more engaging, essentially a remaster of BC's Mount Hyjal raid
=> Make it as challenging as actual raiding, scaling up to 40man, needing a raid leader and all that.
=> Replayability should be allowed like raiding: like if your raid fails to win/defend a base, then it's a wipe and you have to re-do the fight. If your raid stop at midnight, you could continue the Warfront the next day with your progression saved (ie: 3 bases won over 5)
=> Winning a base could give some perks to help continue to progress the Warfront until the final siege, and obviously some epic loot like when you kill a boss in a raid, or/and profession ressources, allowing for extra hard mod (ie "Siege Eldre'Thalas with only 2 bases instead of 5")
----
But whatever route they choose for remastered warfront, the most important thing would be to make ressources shared for everyone in their faction/raid, so when your raid needs to split in order to defend your base, anyone could click the updrage button for your buildings.
I remember when only 3-4 people focused on actually upgrading the Warfront, while the rest was stacking 100+ ressources and never using them, waiting for others to move their asses. No more of that!