As for Sonic X-Treme, that link contains no evidence / sources for an alleged game.com version, so that's a no-go for the website. I try to base all the info there on facts, not speculation.
I've not yet been able to find a source for Sonic X-treme, but I did end up remembering the existence of this
According to Sonic Retro, the above screenshot comes from a promotional booklet* packaged with the game.com itself, so I'd consider that quite definitive. Can we at least add Sonic 3D to the list of cancelled titles?
(This is purely speculative on my part, but maybe Sonic 3D for the game.com was a similar interim replacement for Sonic X-treme, as Traveller's Tales only ported Sonic 3D to the Saturn after X-treme's cancellation? With that already being several months old by the time Tiger was ready to launch the game.com, perhaps they decided it was better to have something approximating the more recent Sonic Jam compilation instead of Sonic 3D? At the very least, I've managed to discover a few shots of various branded electronic items relating to Sonic X-treme, including a portable radio and cassette player. However, I'm fairly sure that I once saw a Tiger-produced handheld of some kind bearing this name, though it might just have been another of the company's many standalone devices, since the first three Sonic games, Sonic Spinball and Sonic 3D all received this treatment. Could it be that I'm confusing Tiger's handhelds altogether, and that Sonic X-treme was actually intended for the R-Zone from slightly earlier?)
*On your site, this screenshot can be found in a 1997 catalogue along with the logo for Sonic Jam, even if all the surrounding artwork is from Sonic 3D. I'm now quite convinced that Sonic 3D was dropped in favour of "Sonic Jam" at the last minute, though I'm still looking to see if Sonic X-treme was ever mentioned as well...