A precursory look makes me think the only thing preventing synchronous rectification using mosfets in DIY alternators would be complexity. The brushless DC motors use Hall Effect switches as sensors, and the placement of these switches in the stator would require some thought and testing. It's kinda like the notion of using relays to switch the coil configurations based on output voltage to achieve lower RPM "cut-in" and higher amperage at some specified higher RPM; certainly can be done, but kinda complex for the average DIYer.
Yes, I have seen Greg's charge controller, very nice piece of work! Many of the parts he sells are below low quantity prices from suppliers like Digikey. (IRFZ44N: Greg = $1.00 Digikey: 1 = $2.04, 10=$12.60, 100=$92.17).