It never was possible.
Some people claimed they did, but never could replicate the results. So, if it ever happened (unlikely), it was due to an intermittent bug, that might have been quashed as long ago as AoS.
On the other hand, if the weapon ONLY has elemental damage, no other properties, and was found as loot (not crafted), there's a chance it might still be allowed for reforging (some items will, some won't), and you could try reforging with one of the properties that can potentially add elemental damage, and pray. Crafted weapons with such properties cannot be done that way, if crafted after the changes to runics that went in around the same time as reforging was introduced.