Hadn't heard of Xfab. Very cool! By older nodes I meant like 28nm or 40nm. Looks like their smallest is currently 0.18 and that nodes been around since before I was even in school! It's definitely still useful for some applications, but not very competitive in my areas.
180nm and bigger is just fine for a lot of things--especially analog or MEMS.
Lots of guitar pedals would be interesting and they can use old school 1um+ technologies that tolerate +-9V. Low power stuff actually likes larger transistors as they have much smaller leakage.
There's lots of interesting stuff to do if you can sink the NRE. The problem is that the super expensive CAD tools don't let you amortize something that isn't a million+ units.
