Perhaps I misunderstood the OPs question - when I read 'Metabones' I automatically assumed he meant the speedbooster. If not, then yes there are plenty of other adapters available at various price points to adapt M42 lenses to the X-mount.
"Speed Boosters for ALPA, Canon FD, Contarex, Contax/Yashica, Leica R, Minolta MD and Nikon lenses on Fuji X series of interchangeable lens mirrorless cameras are available right now. Rollei QBM and other mounts are in the works."
I have NOT tried this, but it seems likely you could, for example, use an M42 to Minolta converter and attach that to the speed booster.
Sure, I guess you could do that, but why would one spend that much money on inferior quality? It's well known (thanks to Lensrentals) that combining multiple adapters leads to visible IQ degradation, so I'd never take that risk given the steep SB price. Not to mention that SB II will soon be available.
Not all that interesting to me when Fuji has so many fantastic native lenses. Fujifilm had my interest with the bodies, nailed me into place with the lenses -- although the Zeiss I have I really love as well.