Yesterday the EPO and USPTO announced that they have agreed to jointly develop a patent classification system based on ECLA and the IPC. The press releases are here and here.
Both offices have yet to work out governance and operational details of the project, so changes to the USPC are not imminent. Some initial ground work has already been done. Since 2002 the USPTO has been establishing e-subclasses that correspond to classifications used by the EPO and JPO.
Why has the USPTO held onto its classification system long after most offices have adopted the IPC? One reason often cited by supporters is that the USPC is far more detailed, allowing inventions to be classified in about 150,000 subclasses as opposed to about 80,000 subclasses in the IPC. ECLA, which is based on the IPC, has about 130,000 subclasses. Others praise the USPC's detailed subclass definitions that guide patent searchers through the USPC's non-intuitive, complex and arcane structure.
The new EPO-USPTO classification will combine the best of both systems. It will be interesting to see what will happen to the sections of the USPC for design patents (Classes D1-D34, D99) and plant patents (Class PLT).