/Not Signed
...I can think of a few reasons why Supercell might have not implemented this yet. At a basic level, you only have to take a hero down for long enough to miss an entire war if the hero you are upgrading is higher than level 4.
If that hero is the queen, you are -by necessity- a th9 player.
1) Being "pulled" out of a war (you don't really have to pull out of war with an upgrading hero; your hero still defends. You just have to have good clan management for target selection) makes it so that it takes longer for you to hoard dark elixir for your next hero upgrade....so it extends the grind towards maxing out your heroes.
2) Perhaps the reason they have not enabled everyone to war with heroes even while upgrading is specifically to temporarily pull the attacking power of high level players down to provide some fluidity to the overall game environment.
3) Perhaps another reason they have not enabled this is to require enhanced cooperation between clan leadership members. Especially with clans that have more members than they war with, it also encourages clans to put bench players into their wars while top players in a clan sit themselves out (again, there's no requirement that you pull yourself out of a war while upgrading a hero)






