Heroes usable while upgrading -- at least in CW

Now that I've got my heroes to levels 19 and 20, missing out on a hero for war attacks is hurting a lot more than it used to. I just don't see any reason heroes need to be out of war, especially for 7 days at a time. It becomes a serious handicap, especially when our top players are upgrading (we have 5 TH 10s, and a lot more TH 7-9s). I've considered gemming the upgrades sometimes during close wars, but that would basically wipe out my gems for what is not a significant enough boost to guarantee a victory.

Alternatively, what about lowering the construction time in general? Maybe down to 5 days (if not less)? For me, I'm to the point where my builders aren't working all the time, so the shorter construction time won't make my heroes level faster, because I don't have the dark elixir to keep upgrading constantly.