But it won't look like one.
I now understand what you're saying. To be fair, NONE of the Flashbacks have ever looked genuinely close to the real thing. They've all been inspired by the original design, i.e., designed to remind you of the original without actually replicating it. The Sega Classic Console and Classic Console 2 clearly have a design inspired by the original three consoles and they even come with modern replicas of the original six button controller.
Frankly, for these to look like the original consoles, there would have to be a LOT of excess plastic and empty space inside, which really doesn't make a lot of practical sense (it's not the real thing after all). The "motherboards" are actually quite tiny in these things.