The best case solution is that services stop requiring ID, problem solved, but ID requirements are just getting worse every year. Second best case is if the UN would issue stateless IDs for people who can't get documents from their country of birth/residence, but this doesn't exist (Nansen passports were discontinued in the 1950s with no replacement). Third best case, a NGO issues substitute IDs which are accepted on a case-by-case basis, but this also doesn't exist. Clearly a "DIY ID" is unlikely to be accepted in real life, which makes the self-declaration more of a philosophical thing than a practical use case.