Outside the ETH ecosystem? I’d say BTC is the obvious next step, but personally I would love to do a Dogecoin integration because wow. such awesome. It was my first taste of the cryptocurrency world, so Doge holds a special place in my heart. I’m also partial to Stellar Lumens (XLM) but it’s pretty far down the list.
Within the ETH ecosystem, I’m looking closely at Chainlink’s oracle protocol and how we can consume their output to create markets. I’ve got ERC721 under control, but I may need to make some tweaks to do the Cryptokitty fractionalization I mentioned earlier, even if it is silly. I’m also impressed with the Enjin 1155 token and everything they are doing, so I’ve started that research as well. I think game items will be quite valuable to the ecosystem in the future.