and if you really want to dedicate the computer to the one application, and risk a bug in it taking out everything and locking the machine up, you can do so. use the root pivilages that you have to give your application realtime priority, they you can keep control of the CPU as much as you want.
just don't consider the result a general purpose system, it's become a dedicated appliance that could be totally useless for anything else.
in fact, other than possibly the need for drivers, you are better off going with something like DOS for your appliance.
that has a place, but it also will have zero effect on the linux distributions, because they are not making single-purpose appliance builds, they are making an OS that will run many different things, frequently at the same time. and while people don't like their music playback to stutter, they usually aren't willing to sacrafice the lots of performance when playing games, or running autocad, etc just so that the background music never skips