IMO the cost of entry is too large for home consoles these days for anyone else to get in without a key partnership (e.g. EA, Ubi, SE, etc with a hardware maker). The cost to enter has raised every generation and requires fighting 2 or 3 well entrenched companies with too much experience, mindshare, and publisher contacts. But what sort of company could get into the market? Software or Hardware companies?
Hardware companies... like Samsung? Look at Sony when they entered the market. They already had a publishing presence as well as a hand in home media. Samsung is not as strong as Sony in regards to home CE brand and completely lack the gaming connections Sony had. Sony also was going up against Sega's horrible market planning and Nintendo burning bridges and taking a more closed approach (Dream Team, carts). Intel? Is Intel willing to lose money on hardware to make money on software? And where will either of these two get enough software?
Software companies... MS is the biggest software company in the world and they have had all sorts of pains getting into the market. Since profits come from game software it narrows the task down mainly to publishers. EA is huge, but do they have the quality to drive a platform? Or the compelling exclusive franchises? Maybe Madden... and? EA as a closed platform would violate their history in many, many ways and would have to be a last resort. Maybe a conglomeration of companies like EA, Namco, Konami, Capcom, SE, Ubisoft, Activision, TH*Q, etc could be a model that could provide enough unique and compelling content to make serious inroads and be competitive while keeping the companies profitable. None could do it alone because as publishers they live and die based on game sales and being exclusive to a small platform could kill them. Also, none of them have 40B like MS or the resources of a Sony.
How about Apple? They do hardware and software, but I don't see them entering the home console market in that they are incapable of getting quality games on their own platform, so what makes one think they could design a compelling console to compete with MS, Sony, and Nintendo and provide enough compelling content to not only drive sales but also to get them out of the red quickly?
The only real chances IMO of getting into the console market would be to NOT compete with Sony/MS/Nintendo with a niche device that garners good 3rd party support and use that as a springboard or to first enter the handheld space with a product that is super compelling (features and price) and has a slew of software support or goes the route of the iPod-for-gaming with a niche focus that branches out slowly to complete more head to head.
But overall the cost of entry alone, plus the resources to make a viable product, seem to be outside the realm of any company on the market, although a union of publishers could solve some problems.
That said, having MS (software), Sony (CE), Nintendo (old timer) in the market gives a fairly good representation of consumers and market conditions and offers real choice. This time around all 3 consoles are quite different in many ways.
So the question is: What would a 4th console maker offer to the market these 3 do not or cannot?