Porting *NIX/open source tools on Windows has been a long-time tradition to introduce quality open source softwore to Windows users. Or allow *NIX users to work on Windows.

Personally, I do like Ext3 because you can mount it r/w on many other OSes.

However on a SD card you might not want r/w all the time, or journaling.

VFAT has many disadvantages compared to Ext3, Ext4 and NTFS. It is vulnerable to fragmention for example. Ext3 supports journaling; VFAT doesn't. Ext2 doesn't support journaling. Ext3 journaling cannot be put off. Ext4 supports putting journaling off. So while Ext4 port for Windows doesn't exist right now I think Ext4 will be a good FS to port to Windows. Although Ext4 has to prove itself in the industry it is not beta anymore and its based on Ext2/Ext3. An Ext4 port for Windows has to be very well tested. One can also think of succesors of JFFS2.