First,waiting a year and a half for something to be implemented is nothing compared to how long ago some requests were first asked for, and while the White Queen is alive, it is always winter but never Christmas.
Waiting can be a pointless exercise, there's no guarantee of implementation even if they looked at the idea favourably.
Second, here's what I was going to write, way back then, is it really that long ago?
I think though it might be handy for a short time and only to some, you will have little chance of it being introduced.
A large majority of players are so rich in resources they are not going to worry about wasting Domain Guards, which theoretically would only be needed in a hostile environment.
They will either send small amounts of troops which they can afford to loose, and when using Domain guards, will likely know already how many troops is an hours worth of yielding.
In a year and a half,I figure by now you have had plenty of opportunity to work this out for yourself.
I have a sneaky suspicion, Domain Guards were availble for purchase then, probably are now,and certainly winnable or easily obtainable for the type of players already mentioned.