OpenBSD supports a number of odd and unusual platforms and does builds on them. See http://www.openbsd.org/plat.html. Older hardware can both use a significant amount of electricity and require much more hand-holding than is possible. Virtualization and emulation are not acceptable substitutes because they claim that doing builds on e.g. VAX is one of the best ways to ensure that the code works on VAX as opposed to simply booting on VAX. They also regularly find bugs affecting all platforms that are exacerbated by one particular architecture (think alignment or endianness issues).