I think that's more risky in that most browsers and many intermediate proxies or other traffic inspectors are likely to have special casing around http: (at least) and https: and for most traffic to be over http(s): and a tiny sliver over web+text: seems fraught with more peril than a (fairly small and intention-aligned) abuse of #fragments. Even mail agents, markdown processors, and other text-display applications often have special casing to turn http(s) URLs into touchable/clickable links.

Page authors are unlikely to use web+text: if it means cutting off old browsers from access.