Perhaps I should clarify that when I mean sample format, I mean the particular way to encode the value of a sample. What I was proposing was the use of a single format when processing, for implementation simplicity and guaranteed high-quality output.
I do not have a principal objection to using a different sampling rate or number of channels. It's just that there are useful gains to be had from limiting the number of sample formats. As an example, processing 16-bit integer audio with the volume plugin will currently cause quantization, because the volume plugin does not do dithering.
And when I said that 44.1 kHz and 16 bits, I was talking about mobile context, I admit android flashed through my mind. Did you know that it does not even support any other output format at all? For a mobile device, it is an entirely reasonable output format, and given its other constraints it should be extremely well supported because it's simply the most important input and output format. As we learnt in this thread, N900 people made a ridiculous mistake with selecting audio hardware that apparently uses native sample rate of 48 kHz because that will force them to do resampling for vast majority of world's music. It is possible to do, but doesn't really strike me as especially smart thing to have done.