I've been thinking of what the fourth movie will bring, based on the preview.
>Sonic CD had time travel as a mechanic
>Amy is present, seemingly competent compared to that version of Sonic
>Metal Sonic is mass-produced and a direct 1:1 replica of his game design
Theory; Amy is from the future and came back to the past, the Amy in Sonic's time is dead and another Amy from another timeline came to fix the damage done, only due to shenanigans with time travel, the timeline where Amy is dead doesn't get fixed and she remains dead.
Long story short, prepare for a lot of fuckery and a potential multiverse setup with that particular Sonic continuity.