It can be argued that more companies entering the hardware market might dilute the current competition, but it's surprise contenders like Sony and Microsoft who have already changed the face of the game when it was between Sega and Nintendo. There should always be capable companies striving to enter and dominate the market, otherwise it's a monopoly.
There have been so many iterations of systems over the years that it would be silly to think that it will or should stay within the top three currently. The market in America is left wide open for a reason, and that is so that companies can innovate and create new things.
The console wars should not remain just between the current big three contenders. I think that any company that can build a console should be allowed to place their product out on the market. I think this would give the other companies some competition and be able to allow them to test their product.
The big 3 tend to produce great consoles. However as long as it's financially possible for other companies to create video game hardware, that's a good thing. Variety is good. Choices are good. Hopefully more competition in the video game market will lead to better prices and choices for consumers, and maybe even a little more creativity in available products.
I do not believe the console wars should remain between the current big three. I would love to see Nintendo put out something new and originally, they have a lot of room for improvement and they are generally my favorite, given their standard genre. However, I would like to see more competition in this industry. I think we have a lot of options and a lot of technology to support it, so it should be doable.