Jothar, I have strong doubts about that line of reasoning as to what cleaning may accomplish, but by all means ask if you want to. Please find sources if you can for the cleaning you claim they do (incl. how and when); I’ve already commented on this and included sources.
Sure it’s possible to dissect the wood (more accurately, break open a stave). There is literature on the so-called penetration line of a wine cask, and I have seen it (the literature, that is). There are a lot of variables such as the type of wood (European is more porous than American), the size of the cask, etc., but for a standard Bordeaux cask, it is around 3-7 mm after several years of use; for other casks aging contents for many years, it is perhaps halfway through the thickness. The question is if one can rely on such visual evidence halachically for a shiur of bitul. My understanding (not my own) is it would be a tremendous chiddush since we don’t do so elsewhere, so the burden would be on the maikal. And it may be appropriate to ask if this is the kind of kulah a Kashrus organization should be relying on to permit scotch to the masses.