The disadvantage of GW isn't the cork, it's the gluing of a canvas "feather" to which the welt is sewn, to the insole, as opposed to sewing it into a hand-cut groove. Cork is a good and proven base for the footbed and can happily last as long as the leather sole before being replaced at the same time.
The only alternative to such fillers is to use a full leather midsole instead of a welt, as with the Blake Rapid construction - that although machine stitched, does away with the glued "feather". I believe our own village elder Mr Frommer is even a fan of this as the best mass-manufacture construction method.
But this is not the proper thread for this. It is just revealing to me how the HW Meermins really look like from the inside.