So, I know that you are not supposed to use code-based item rendering in 1.9, and instead use models. I respect that, and this is more of a hypothetical, but plausible, situation:

 

A game has a spell system. Spells are objects which have a model for inventory and world, but when held in the hand is represented by the player's arm and a dynamic, GL-based effect (think ender dragon death animation/end portal animation).

 

Is this at all possible in the new system?

Sure.

 

Ah - OK. I was not sure if the new system had made it impossible to do, rather than just discouraged.

Well, you cannot actually do direct GL. You have to do it via models still.

 

Ah - well that is what I was asking - if it were possible to do rendering in GL for items for items which require freaky effects to pull off.

You can always use rendering events to detect if given item is worn and apply animation/effect to player. But that will be only useful if you want to e.g: render spell-orb in player's hand. Not really if you would like to e.g: have sword glow.