These brokers are getting goofy with what they allow and don't allow. For example, Interactive Brokers for the longest time did not allow GBTC trading, but did allow COINXBT (XBTProvider ETN) trading. Now they don't allow COINXBT to trade, but do allow GBTC and bitcoin futures trading. Hilarious!

And people wonder why GBTC trades at a premium! A ton of money has lost access to COINXBT which traded close to the BTC spot. These brokers are exacerbating the problem.