Toyota has included these "Cyclone Pre Filters" on several of their models over the past few years. The concept is similar to that of a Dyson vacuum: the air is accelerated in a vortex which flings the particulate dust out into a trap. This reduces the particulate matter that makes it to the actual intake filter. Here's a link
showing the Toyota assembly.
Anyway, has anyone retrofitted this type of pre-filter to their WK2 (not necessarily the Toyota part, but an equivalent technology)?
P.S. This is a relatively common technology these days... it is even available for shop vacuums.