It's a nice idea and you've thought it out well but I can't see this being added into the actual game anytime. A mod for this would be really cool though.
I agree that hoes are relatively unused and I rarely (if ever) actually end up crafting one, but there are supposed to be some farming updates in 1.8 so it is possible things like this and changes to it will be considered and implemented.
I think mirrors should be implemented along with a two-way mirror so that on one side it is transparent and on the other it doesn't appear so, this would be useful for "secret hideouts" or hiding places. Mirrors in general would be interesting for decoration and potentially for different lighting options.
Adding some more machinery and functions to them would be interesting. Perhaps something like generators, farming machinery, transmitters, communication machinery, things along that line. They would all have to be fairly difficult to make.
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