No
because of the following reasons
-
Sega isn't what it used to be. They simply don't have the capital to design, manufacture, market and support a console. They're barely surviving as a publisher.
-
As said earlier, there is no room for a fourth console. What role would Sega have to take? The powerhouse console? PS3(/4) says hi. The affordable console? The Wii/Café says hi. The motion gaming console? MS, Nintendo and Sony say hi. The awesome arcade, 2D-style game console? That would be so awesome. But too bad that's something of the past. People want visually stunning games, FPS's preferbly.
-Sega doesn't have the resources to make killer-app, exclusive games for their own console.
EDIT:
Wait. I've got a brilliant idea. Sega should make modern arcade cabinets. That's a hole in the market. A blue ocean strategy!