Daelo, the Lead Encounter Designer, announced today that the debuff limit has been removed*. This is a subtle yet important change for many raiding guilds.
He notes that the default UI won't normally be able to show all the debuffs, but that's just a bug in the UI. The debuffs are still there and working. We don't have any verifiable information yet as to if custom mods can display an infinite number of debuffs.
It's interesting to note that back in the day there was a limit of 16 debuffs. That was increased to 40 for the Burning Crusade expansion in 2007. And even before that there was a limit of 8. Elizabeth Harper talked about it in an article back in August of 2006.
Oh how the times have changed.
*It should be noted that Daelo said the debuff limit has been "effectively removed." I take this to mean that the number of possible debuffs on a mob is so high that no one can possibly reach it. The way games are built necessitates a limit on all numbers due to restriction on numerical data types in the programming language / computer system. An example of a hard coded limit on a seemingly infinite item is how much gold you can have. Daelo is likely referring to this situation, in that there is some "upper bound" on the number of debuffs dictated by programmatical means. But don't fear, even if the number of debuffs is contained in a byte-sized array, you're still looking at total possible debuff limit of 255 debuffs. More likely the debuff list is kept with a 32 bit word-sized array, in which case the number of possible debuffs would be 2,147,483,647 if the word is signed (which is likely the case given that gold is stored in a signed word), or 4,294,967,295 if the word is unsigned.