A speedbooster is, in essence, a kind of reverse teleconverter- its a converging group of lenses, rather than a diverging group, like a teleconverter. That doesn't mean that a speedbooster is literally a reversed teleconverter, or that you can achieve the same effect by mounting a teleconverter backwards, if that's what you're asking. It's certainly theoretically possible to design a lens group which adapts medium format lenses to 35mm in the same way as a speedbooster is used for APS-C and MFT, but like others have noted, I don't think such a thing exists currently, and adapters for P67 lenses and others generally don't have an optical component, they just get the flange to film distance right and make the mounts compatible.