I have to admit that I struggle to figure out quite what's perceived to be so "ridiculous" about most of the examples so far quoted (of which, incidentally, the Sorabji one is indeed from OC's Passacaglia). The notational "conventions" of Xenakis's Synaphai are admittedly pretty resistant to easy figuring out, either from the standpoint of klavierfaktur or visual intelligibility, but even that is merely a part of what has to be taken on board when Xenakis writes something of which near-accurate representation of the text as presented is arguably less of an intended issue as is the case with much other piano music (and that remark, for the record, is not meant as a pejorative). Roslavets's use of accidentals in his piano music written around WWI can sometimes make for difficulties of reading and perhaps offer at least some would-be interpreters undue temptation to rewrite passages (rightly or wrongly in principle) so as to make them seem rather easier to prepare. The fact that there are few ways in which to rewrite the Stockhausen or Rzewski examples to make them seem to appear any less "ridiculous" is itself suggestive that they're not as "ridiculous" as some might at first think. Alkan's occasional oddities of accidental use are hardly "ridiculous" - just rather unusual and not that hard to figure out. The very citation of Scriabin and some others here in such a context is more "ridiculous" than the examples themselves could possibly be! What's so ridiculous about the way in which the Sorabji is presented? The immensely effective closing pages of Yedidia's Third Piano Sonata, whilst a real test of the pianist's hand/eye co-ordination in practice and replete with obvious dangers, are hardly notated in a "ridiculous" way. Hamelin's quotes here have absolutely no place to be cited in the context of such a thread as this; that's just plan daft.
So, all in all, what's the big deal?
Best,
Alistair