The only telescopic blanks I've seen are pretty low quality and aren't designed for casting flies so I'm not sure how well they'd work for tenkara. As far as bamboo, I have a split cane one I had custom built. It's too heavy (and tip heavy) to really be practical. There's a reason why they used hollow bamboo for traditional tenkara rods.
_________________My blog: Tenkara TalkTenkara USA Rods:
Amago, Ayu, Ayu Series II, Ebisu, Ito, Iwana 11', Iwana 12', YamameOther Tenkara USA Gear:
Tamo, Strap Pack, 3.5 & 4.5 Level Line, 10.5 ft. & 13 ft. Traditional Line, Line Spools