When I have my composer hat on I am always interested in writing music with complex rhythms. There's a lot of fun to be had trying to play weird time signatures and note sub-divisions but the problem is finding other musicians that share this passion.
Generally, musicians find rhythm 'difficult'. I've played with some extremely talented musicians who get 'stuck' when it comes to rhythms that are a little more intricate than maybe they are familiar with. Certainly, complex rhythms are harder to sight read but that doesn't mean they can't be played! Counting the rhythm out is always the first step; however, it's also important to be able to 'feel' a rhythm.
Take for example, playing a triplet, a three-note subdivision. Most people can feel a triplet even if they aren't a musician. But what about a quintuplet… that's a five-note subdivision, where you play five notes in the space of four, e.g., five semiquavers instead of four. That's a little bit harder. It's harder still to play five notes over two beats, i.e., five quavers in the space of four (if we're in 4/4, that's five quavers in the space of two beats). I've always practised 'feeling' these sorts of rhythms because you can't really count them out. They're not easy to play accurately either. Feeling them is the best way… with a metronome clicking away, of course.
Here's an example of a piece which contains some fairly odd sub-divisions. I'm learning to play this at the moment and although I'm getting close to nailing it, I still find it hard to play without a click.