i just checked and the 2nd disc of The Hulk (the dvd movie) does indeed have a default.xbe sitting on a UDF formatted disc. so, whatever possibilities are opened here, they've actually be sitting there waiting for us for a long time

here are the contents on The Hulk (dvd movie disc 2)
default.xbe...size=124,624kb
\xboxdash\
...default.xip...1509kb
...dvd.xip...164kb
...jkeyboard.xip...716kb
...keyboard.xip...643kb
...message.xip...783kb
...settings3.xip...2743kb
...settings_clock.xip...1645kb
...settings_language.xip...1397kb
...settings_list.xip...2861kb
...settings_panel.xip...2669kb
...settings_parental.xip...985kb
...settings_timezone.xip...1340kb
...settings_video.xip...1932kb
...xboxdash.xbe...1532kb
comparing to my 'backups' of the 4034, 4920, and 5960 dashes, this is neither...
it would seem like the stuff on Hulk has a greater possibility for exploitation since it's older, but perhaps wouldn't work on boxes where kernel >= 5713