Hardware's just one thing. I'm sure Sega-Sammy could scrounge up enough venture capital and whatnot for a decent-enough launch at least of some kind of new console. However that's the easy bit.
You NEEED killer software also or you're deader than fucking DEAD. Where's the triple-A titles that will carry this mythological beastie? Sega has no talent anymore, no mindshare. They've tried to live off of the reputation of Sonic, but all they've managed is to screw up, repeatedly...
Also, to survive past the 90-day launch window (roughly speaking), you need a decent enough third-party following, you need a huge development and support mechanism or else other devs just aren't going to bother with your platform, especially since any new hardware will start off with an installed customer base of ZERO. You need a resident firmware; easy-to-use, powerful, yet light-weight. The OS must have APIs for all the things you can reasonably expect a games console to manage these days.
Also these days you need a working, solid online strategy. You need login servers, cloud storage for all that achievement crap that's so popular these days, friends lists and whatnot. You need an online store, with strong DRM to protect the stuff running on your platform. Again: or else nobody will bother to develop for a new untested platform.
All of this will need to be stress-tested, and tested again. It has to work once the launch goes off, you can't have news that your DRM can be circumvented by - for example - a specifically crafted/corrupt file on a USB stick or something silly like that.
If these things are missing then there's just too much work and too much risk for too little profit, and no third-parties in their right mind will bother with it.
Ensuring all this would cost craploads of money. I wouldn't be surprised if it didn't end up costing at least as much if not a lot more than manufacturing and shipping out all the hardware launch units.
And of course, regardless of whatever I may have missed in this post, there's simply no room in the marketplace for another console. That's just the way it is.