AM1808 revision 2.1 has been released, and booting from MMC and SD devices is now supported.
See the updated Bootloader Application Report for details on the various features and modes supported.
In addition, a wiki has been created to compare boot times among the various boot modes supported on revision 2.1: Boot Benchmarks
If you have any questions, feel free to ask below and we will do our best to respond. Thanks!