I'm not sure where you received this information, but the next version of BE will not let you change from SQL instance to MSDE on the fly.
Typically you always want to install in an MSDE instance if for no other reason, the SQL Master cannot be restored while BE is using it, therefore if you are doing a full system recover, it will take more steps to do the restore and invovle unnecessary parallel databases.
I hope this helps answer your question.