The hope is that a standard will be created soon to support this behaviour. These sorts of things are complicated because it requires support of the chipset vendors. i.e Intel and AMD.

Standard or not, making the sockets equal just add to the confusion. You best plug it into the right socket or your system won't even work.

Using a different socket is best in all cases.

How much real-world improvement is there using a DIMM slot instead of PCI-E bus?