Just a small thought here.
Forewarning, I've never done an animated one before :/
If you have the tileentity update a counter and every say, 25 ticks or whatever is a decent number for the animation, have it cycle the gui picture, you could get something "animated" with multiple pictures. I think this is probably something similar to how they do it in vanilla, because there are multiple icon tiles for fire, block breaking, etc.
I think you would reference the tileentity from the gui and then get the public int count, and whenever it hits the target number to switch, reset the count to 0 as well. I don't know if this helps :/
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