If that's the case, the thing that qualifies as a "desktop" today seems to be a device that is easy for consumption (HD screen, loud speakers etc), is portable (under 18in?), and can last through a couple hours without continuous power source (battery dude)

Hence, the closest thing to a "modern desktop" would be a Win8 PRO tablet that can dock for a keyboard and power. Top example would be the Lenovo Helix. It has "Desktop Apps" as well as the basis to do future desktop "stuff".

WinRT is a no-go. I don't mean to knock it down, Microsoft has really been clearing bugs.

#rant
But the SurfaceRT wa- IS a bad product. That kickstand is a waste of space and weight. Corners are too sharp or is it the odd shape/size. Screen is lacking. Tegra3 seriously? They should've gone with at least a Dualcore S4 (same performance, better efficiency)... or a Exynos 5xxx (A15 powaa). MS has tripped itself again #rant

This results in a glacial market share of RT, means its not producing interest for developers and "future desktop stuff" at a competitive level.
It basically means MS wasted its effort, money, time to fix up RT the last year. It could've improved it at a slower pace, and it wouldn't affected its "ecosystem health". Currently, its possible for it to even die as a platform.

If RT does get traction.
If more powerful ARM SoC's are supported.
If MS squishes more bugs, adds missing features.
...then Yes, a WinRT hybrid can displace a Win8PRO hybrid as a desktop.

Then the definition of "dektop" can change.
We might have true-dektop grade software in a more device that's more portable, lasts longer and performs much faster.

Until then the iPad is a glorified consumption device.
Android needs another generation leap (or two!) to even begin to cater.
And a gaping hole in for a Linux ecosystem for "todays desktop" is ever increasing.