The issue here is the amount of hardware that needs to be bought for a CPU algo. For a GPU algo, all you need to increase hashrates is to buy the GPU and riser card. Now, you will have to get the whole shebang (PSU, memory, MB etc.) How will this be ever profitable? Will there ever be a riser card/board equivalent for CPUs?
That's all part of the cost per hash. It's no different than an algo with a lower hashrate requiring
more CPU (or GPU) power to produce the same hash. What matters is how much the hash is worth.
Yes Intel has Xeon Phi compute addin boards with up to 72 cores with 4:1 hyperthreading
for 288 threads. The're compute beasts but very expensive and not suitable for mining due
to the low mem/thread ratio. It maxes out at 384 GB which is similar to the cache/thread
ratio of most desktop CPUs.