I would like to see support for booting FreeBSD (or Linux as well) diskless from a net server.
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So this request really is for netbooting a BIOS-based OS. The BIOS emulation in Apple's firmware apparently doesn't support this, and rEFIt has no direct control over that, so this means a major undertaking.
In the meantime, see http://forum.onmac.net/showthread.php?t=1754 for some ideas how to do interesting netboot things.