I doubt we ever see a desktop class GPU in the iMac.
Think about how a desktop GPU installs and then think about the inside of an iMac.
First, the desktop GPU would need to be a custom design for Apple. There would be no reason to have video outputs such as HDMI, DVI, DP, etc., directly on the GPU. In addition, the GPU uses a PCIe 16x connection. Why would they want to take up so much room in an all in one with such a long connection? Second, the heatsink/cooling and mounting brakcet on a typical desktop GPU is designed as if it were to be mounted inside of a typical ATX case (and its variations, ITX, mATX, etc.)
A mobile GPU makes sense for the iMac. The MXM slot instead of a traditional PCIe slot is smaller. The video connector found on a mobile GPU makes sense to be used for a unit with a built in monitor. The list goes on.
Basically, if Apple were to use a desktop GPU in the iMac, they would have to reinvent the wheel. Which they have done for many products and features many times, but this time it doesn't make sense when Nvidia or AMD offer something that fits what they need, i.e., a mobile GPU.
Think about how a desktop GPU installs and then think about the inside of an iMac.
First, the desktop GPU would need to be a custom design for Apple. There would be no reason to have video outputs such as HDMI, DVI, DP, etc., directly on the GPU. In addition, the GPU uses a PCIe 16x connection. Why would they want to take up so much room in an all in one with such a long connection? Second, the heatsink/cooling and mounting brakcet on a typical desktop GPU is designed as if it were to be mounted inside of a typical ATX case (and its variations, ITX, mATX, etc.)
A mobile GPU makes sense for the iMac. The MXM slot instead of a traditional PCIe slot is smaller. The video connector found on a mobile GPU makes sense to be used for a unit with a built in monitor. The list goes on.
Basically, if Apple were to use a desktop GPU in the iMac, they would have to reinvent the wheel. Which they have done for many products and features many times, but this time it doesn't make sense when Nvidia or AMD offer something that fits what they need, i.e., a mobile GPU.