AFAIK the beaglebones load their entire executable environment, including bootloader, from removable flash media - there shouldn't be any bravery required to test out experimental software (even bootloaders and firmware) because you can always just swap out the entire card. There's no bricking them.
Yep, they can either load from removable flash (microSD) or from onboard eMMC flash storage, selectable by switch on boot.
Students at UNSW doing Advanced Operating systems use a SabreLite board running seL4. They're pretty similar so you should be able to get it working.