A quality FW800 enclosure will cost a good amount of money. The FW800 chipset is expensive, and the end user pays for it. We (Icy Dock) have a couple different FW800 enclosures for a single drive, and they are on Newegg for about 70-80 bucks, and then you still need to get the drive.
/shameless plug 😉
I would definitely agree that you will spend about 90% less time troubleshooting/dealing with issues with FW800 over eSATA though with OSX.
And I doubt Apple will ever fully adopt USB3, seeing as they are supposedly developing both FW3200 and a new interface that will be combining about 3 or 4 different interfaces into a single connection. However, they are in bed with Intel now, so USB3 just might be on the horizon. Either way, they are not saying anything about it, as usual.