I love the thumb on my PC35 excavator. Much more useful on that type machine than a tractor backhoe attachment. A 4 in 1 front bucket on the tractor/backhoe is the way to go IMHO.
"Real" thumb? As with most everything else, that's already been done on a Kubota BX
The pix start at post #63 at this link.
There will probably never be another one like nasdaqsam. Search for his articulated BH-mounted rake for another amazing tale.
Cheers!