I agree, but it's possible that they've just not committed it to other platforms at first; the Sonic CD game rolled out to some other platforms over time, so hopefully they're just not over-announcing its targets. (The fact that Wii U isn't among the consoles though is a real shame, especially since Sonic has nestled in on Nintendo platforms for a while now and NX is a target for the next game.) Then again, as E_Darkness pointed out, Sonic 1 and 2 Remastered stayed on mobile...
Curious, what is the difference between Christian Whitehead's
Retro Engine and the
Headcannon Game Engine (HCGE)? Same thing? Companion component engines?
I tried to read up on HCGE to see what it can do, but aside from talk of the Sonic mobile games, there's not much about the engine itself on the official page/forum since 2014. And Taxman's most recent update talks about doing Unity programming work for the Freedom Planet 2 team (though that's its own thing and sensibly uses the team's choice of engines.) I believe I've seen people post about HCGE and Retro Engine on GAF independent of the Sonic projects, but I don't really know much about what the technologies aside from that they made for amazing Sonics, is there more to know?