Most likely no. I highly doubt Sega would stand a chance in today's console market since the bar has been raised pretty damn high for anyone willing to come in now. The 360 and PS3 would be hard to contend with graphics and hardware wise, they're beasts and considering how well the Dreamcast did I doubt they'd be able to make something up to those specs.
Though the Wii is doing well we have to look at it from a different aspect then power and hardware. Considering the Wii is just a Gamecube slimmed down (graphics wise, I do realize there is different hardware on the system, I just consider it a slimmed down GC) it doesn't hold well in that market. Wii's success has to do with it's family appeal and innovative controller (as much as I hate the Wii-mote I admit it's pretty damn innovative). This is the main reason it's outsold both the 360 and PS3.
Should Sega one day decide to come back onto the console market it's either going to have to build a powerhouse machine to contend with the PS3 and 360 or it's going to have to go the same way as Nintendo did and make a console that's more family oriented. I don't really see Sega being able to pull this off from both a designer mindset nor do I see it from a consumer mindset. They'd have to make some pretty big changes to come back into the console market and I just don't really see it being possible for Sega.