Innovation
This new market would be highly innovative and very competitive because of the low barriers for companies to enter such market. Any new company entering the market would not have to reinvent the wheel to get on par with competition, but could instead focus on standing apart from the competition or bringing something better then what is currently available. So the focus of innovation would actually be allowed to reach further and would probably transform the market and make it compelling for even more customers.

Complications
Obviously this is not in everyones interest, companies generally have no benefit of the creation of such an open market. It will be much harder to hold on to market share and it will be harder to be profitable in this market. It is impossible to lock in customers in such a market as the technology they use is freely accessible by others.

Example
If we look at gaming for example, this is a divided market, there are currently 4 gaming platforms: PC, Wii, Playstation 3 and Xbox 360. Whenever a customer chooses one of these they are pretty much locked in for the current generation of gaming platforms, since games are not exchangable between these platforms. One could of course buy multiple gaming devices but why would you want to? I only have one microwave oven, not one for each type of food… So an open gaming market would mean no company can control the it and every company would have to compete by creating good games.

Why isn’t this happening?
I think this isn’t happening now because no single company controlling a market is willing to give up their estabelished market share or dominance. Another point is that people are probably still having trouble with the openness of the internet, so much choice for endless supplies of content. But also there is no single entity to blame if something doesn’t work for the user when the user is doing something wrong. Closed markets are perhaps more comfortable or at least easier to comprehend for users.
There is at least one company who would prefer an open gaming market (or stated to want one), but do note how this is a content distributor and not Nintendo, Sony or Microsoft (which control pieces of the market): EA wants ‘open gaming platform’.