Beyond3D claims the ATI Radeon X1900 GT will soon get a specifications change. The clock speed will be decreased from 575MHz to 512MHz, while the memory speed will increase from 600MHz to 660MHz.
A PCB redesign is also included to accommodate a fan change anticipated to produce improved acoustics, and HDCP capability is included by default on the new boards.
So, in exchange for a modest core decrease, purchasers of the new board will get faster memory, a hopefully quieter fan, and HDCP. As partners are expecting overall performance to remain pretty close, this doesn't sound like an unreasonable set of trade offs to be making.
Unfortunately, by deciding against a new name ("X1900 GT SE", anyone?) the situation becomes rife for some confusion for individual purchasers. There will be two significantly different "X1900 GT" abroad in the land, and consumers who care about the difference between them should be careful to determine they know which they are purchasing until the stock of the old model disappears completely.