Demo of MeeGo/Maemo dual-boot
Carsten Munk, maintainer of the MeeGo N900 adaptation project, has posted a quick video showing an N900 dual-booting between Maemo 5 and MeeGo 1.1: Many thanks go to the MeeGo N900 hardware adaptation team for all of their hard work in making this possible. He's also described that the plan is along the lines of having a Maemo-installable package which will detect the presence of a memory card which, if present, will boot into MeeGo. In your editor's opinion, this is still a little clumsy (compared with the bootmenu approaches) due to the need to keep your MeeGo-touting MicroSD card handy, but not installed. Given the N900 back needs to be removed to insert or remove the memory card, this may be an elegant software solution; but not necessarily particularly graceful in practice.
However, a variety of approaches will be possible, after the proof-of-concept is released; and those who prefer a bootmenu-style will - no doubt - be catered to.