Honestly, a laptop gpu in desktop form might be interesting for small form factor or power limited desktops. That is really niche though.
The concept is'nt new.
What you see here is a PCI-E MXM module that can hold up to 2 MXM GPU's working in crossfire.
But looking at the costs a real desktop GPU would be better.
And if you have plenty of money, you can actually pay someone to "design" you a custom based PCB:
A 4x Polaris (RX480/RX580) on a single PCB.