I plan to, if the customs I'm getting turn out to be better than my current setup.
I agree, fans are incredibly loud, and I don't want to hear them when no music is playing.
Its also great to have one headphone for portable and home use; simplifies things. I can pour all my budget into one thing rather than split it up and compromise one side. I mean, getting just a mid-fi headphone (ie. HD 600 / K701) + amp + dac costs as much as a top tier custom. Why not go the custom route instead?