does this have actually any future in curl? I remember the rust http implementation getting deprecated (or already removed?) because of lack of interest and maintenance?

I think it's a different situation. From my perspective the foundation for alternative TLS implementations in curl is more robust than for HTTP. To date there's been no discussion about removing rustls curl support. I expect it will stay in experimental phase until rustls itself is 1.0 (work in progress) and then hopefully graduate to a stable feature.