This is just a concept, but perhaps can lead to a community-driven and open source project that tackles Bitcoin's Energy Efficiency problem. The project, which I dub "Bitcoin Efficient", might do just that, and much more. Unlike other hard forks from BTC such as Bitcoin Cash, Bitcoin Efficient aims to have dramatic changes in regards to hashing and consensus. The project aims to change the way Bitcoin is being mined.
The primary focus of the architecture is a consensus dubbed, "Proof of Computation" or PoCP. In short, I've described it as the following:
Large entities worth billions upon billions of dollars are building data centers filled with ASIC rigs. Most computers can't efficiently mine BTC, and you have high energy costs. Outside of energy costs, Bitcoin isn't as efficient as it could be. You have slow speeds, many invalidated blocks, and the network extremely vulnerable to centralized mining. This is where we introduce a hard fork known as Bitcoin Efficient. Bitcoin Efficient aims to allow everybody on board without disenfranchising ASIC miners. This aims to be much more energy efficient, decentralized, and take adaptability to a whole new level. It will be based off of "Proof of Computation" over just Hashcash.
You have multiple problems that need to be solved in regards to how Bitcoin is currently mined, and how it isn't just energy consumptive, but vulnerable to monopolization and censorship. Part of this is that the extremely centralized nature of its mining, can give specific entities and even certain chip manufacturers a heavy advantage from the very beginning.
Some of these same entities may block certain BTC transactions from being mined or going through. This problem, and the fact that we have many invalidated blocks, billions, maybe even eventually trillions of dollars in lost gas fees, and the only supposed solution is alternative energy, means that there needs to be a better way.
Even if Bitcoin was largely powered by alternative energy in the future, the way it goes about block validation could rapidly improve. If done in a way that doesn't disenfranchise anybody or sacrifice security, that could be a huge step in the right direction. This is why Bitcoin Efficient was started.
Other cool open source projects are also taking some initiatives. I still think Livepeer and Chia has some pretty cool technology, Siacoin also seems quite promising along w/ networks like Crust. Even though, I am working on some similar things, it is nice to see other players in the field. The more players and competitiveness, the more open solutions that are out there.