While there are no functional changes to these cards [Professor Juniper and Professor Sycamore], you may not include both of them in your deck. That is, you may have up to 4 copies of Professor Juniper or up to 4 copies of Professor Sycamore - but if you have any Professor Juniper cards in your deck, you may not put any Professor Sycamore cards in your deck, and vice versa.
Source: TPCi Announcement (2013-10-01), TPCi Rules Team (2013-11-21)