Yep, I skipped mentioning the "Do you want to play the {optical disc}" message. But that is what I would prefer, if the "Enable Blu-ray Menus" option is selected: Ask if I want to play, when I select yes, play the Blu-ray as if it was being played in a hardware Blu-ray player, which means all the warnings and rubbish, if present, are played, and then the Blu-ray menu is displayed.
If the "Enable Blu-ray Menus" option is not selected, then the title track of the Blu-ray would be played.
If a Blu-ray was being played, the menu button would return the user to the Blu-ray menu, possibly at a lower level menu such as an outtakes sub-menu, just like a real hardware player. I haven't actually used a Blu-ray or DVD hardware player in years and years, but from memory that is what they do. Depending on the optical disc authoring of course.
If the OSD up/down arrow could be used to access the Blu-ray menu or the title list, that would be my prefered method.
If you had to use the menu button while a disc was playing (either a title or the menu) to access the menu or title list, then I would accept that as it does provide more flexibility. But it would be inconsistent with a hardware Blu-ray player experience I think, so may cause transitional problems for users learning to play Blu-rays in MC.
Basically, the Menu button acts like a traditional hardware Blu-ray player, while the Up/Down Arrow OSD acts like the traditional MC OSD menus.
A user wants the Blu-ray Menu (at any time) they press the Menu button.
A user wants the title list in a playing Blu-ray, they press the up button, or if the Blu-ray menu system provides a title list, they press the menu button to get back to the Blu-ray menu, and then navigate to that title list.
It's always good to get the groundwork done on deciding what the endpoint will be, so that development isn't done that would lock out the best solution. Hence, I am sharing my current feelings.