I feel as if this may have been posted, but as you can see this is my 1st post and am new to the forums but I did not see anything when using the search function. Also looked and didn't see this in the previous suggestions/ruled-out thread.
I think when in a Clan War, heroes should always be available to attack regardless of if they are upgrading. The reason I think we need this is Heroes are powerful troops, and not having them available because a player is upgrading hurts the rest of the clan just as much as the individual when trying to accumulate stars. This is already implemented on defense with not only heroes but all defensive structures, and I think it should extend to the offensive end as well.
Note that this idea applies to Clan Wars only and not normal raids. In single player mode, I have no problem with being handicapped on defense or offense when upgrading something, but that only affects me. Clan Wars can be expensive for players to fund costing a lot of elixir and DE to provide troops, so just give us the best chance at getting back our investment for ourselves or others by not giving us a penalty when upgrading the BK or AQ.