You can't just take only the benefits of system memory and embedded/package DRAM and make something out of it. Idontcare, you have given a good example of balancing in this post:
http://forums.anandtech.com/showpost.php?p=33158287&postcount=40
First, I'd like to add to his post that it only applies when we are looking technologies that are at cutting edge. For example, we can only say RAM is faster and greater capacity than SSD when comparing relatively recent examples(5 years or less). It may not be true in the case the RAM is from 1980's and SSD is from 2012.
If you can make RAM that's really really fast, then you can make that into embedded memory and make it
even faster. So that advantage is always there. You can't beat physics, so its impossible to make memory that's farther away faster than one that's closer.