Basically, once fusion power is achievable, this currency effectively loses all value, indefinitely. Electricity will be infinite so this currency well also be infinite.
Really? You're assuming that we won't have to pay for electricity; this world is a giant business and the people who end up controlling the technology will be the ones to profit from it. Certainly won't be a charity thing. And again, Bitcoin is not "infinite". There is a limited amount that can be made.