Another idea:

I have an 600D and the pierogi remote works beautiful for single shot photos. Timelapse is nothing else than repeating the same command with a certain interval... Right now timelapse only can be done using a usbcable and shoot tethered with my laptop. Doing this with the N900 would be much more comfortable than carrying around a laptop and a clumsy cable.

So my question would it be easy to implement a timelapse possibility without buying a expensive remote?

Maybe this would be better as a small fork which is only meant for controlling cameras, as i have seen other camera keysets as well.