There is quite a bit of demand for Bitcoin over illegal goods markets. The thing is though, buying bitcoins in the ways the black market would prefer usually comes at a premium nd other than that, the fact that correlating Bitcoin transactions to the type of activity they support ilmakes it difficult to compare the effect darknet markets have on the price over speculative markets.
Hmmm as far as I know the demand isn't exactly rising, on the contrary.
Last time I checked Alphabay had 3 coins to trade with. It's not like when Silk road was all that mattered, now even illegal merchant sites know what they're doing and they're actually working with multiple coins as long as it guarantees a certain security level.
Monero was used largely for example.
Don't think btc is the only thing used for that kind of stuff xD