They got rid of that whole idea. I think it's because nobody would bother breaking down an epic (I assume the prices would rise rapidly) just to obtain a potion that wouldn't be of 'epic' standard (Light foot for example, the maximum level being 500)
The composing thing does not raise prices on all items.
It merely creates a (flexible) minimum price on items.
For example, an item that was worth 100 FSP will still be worth 100 FSP now that composing is here. And an item that was worth 1,000 gold will now be worth 20,000 gold.
No player would even be thinking about buying an item that is worth 100 FSP to break it down into fragments when he can also just buy a much cheaper item.
The existence of composing just raises the prices on very cheap items to a level that players are willing to pay for fragments. It does not affect the price of already expensive items in any way.
Most epics are worth quite a lot (100+ FSP), and people will probably not break those down if epics could be broken down.
The only things that might have a reasonably low price that makes breaking down a viable option are the quest epic weapons, the Inferno Hammer and the Steamwork Cuirass, but those are still quite expensive compared to crystalline, SE and LE items.
If epics would be included into the composing system then there would either be a problem of supply because most epics are hard to obtain (compared to other items). There would also be a problem with the price because they are fairly expensive (compared to other items) and that would mean the highest level potions would only be available to the richest players.