It is small enough for now, in my opinion.
When we get to the point in time where a μBTC becomes common denomination for buying goods (like mBTC is now) then maybe it will be time to start thinking about nBTC and pBTC. But we are long ways away from that time, so no need to fiddle with it now.
In my opinion.
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And the smallest denomination of USD being a penny is ridiculous. Our inflationary currency has made them worthless, we really should get rid of them. Hell, I'd even be for getting rid of the nickel too but we can't because of the quarter and dime.
-.00000000000000000000000000000000000000000000000000000000000000000000000001 BTC
LOL !