We can only take full credit for the McLaren renderings shown here - the LaFerrari Roadster is from Garrett Bradford's blog.
But pairing up these fantasy renderings seems logical. Both will heavily leverage the folding-top tech from the 458 and 650S cabriolets, with flying buttresses to house parts of the folding hardtop mechanicals and three-piece folding panels to stack compactly above the engine bays.
Of course, a flatter tail is definitely sexier -- as shown by this unfinished render draft.
So, why Spider versions of these hardcore hypercars?
It is a natural evolution for both, and allows production of an extra-exclusive followup to both coupe designs. This helps amortize their astronomical development costs over more units, while also keeping initial production caps for both intact.
Car-Revs-Daily.com McLaren P1 Spider Rendering
2016 LaFerrari Roadster Rendering by Garrett Bradford
LaFerrari Roadster vs McLaren P1 Spider