The answer to ten man vs twenty-five man raiding is simple. Let raids size from 10 up to 25 -- including every number in-between. Scale loot and difficulty based on in-boss raid attendance. Don't put in mechanics where you have to change them when you only have 10 (e.g.- mind-controlling priests vs mind-control devices).
Scale the number of loot drops. Scale the boss health. Scale the adds. Scale the damage out. Everything is a formula already, just add in a raid size coefficient.
Don't have 25 on raid day one? Raid with what you have. Have more the next raid night? Great! Raid with what you have. Bring the player not the warm body.
Added to the Blizzard suggestion box.