I desperately want a film just so Eccleston can play him, even though I suspect it's an unfilmable book.

That would be very awesome, in a Lynch kind of way. It's not really any more unfilmable than Inland Empire, though of course it'd be pricier. :-)

Though my favourite choice for DWJ filming would be Dark Lord of Derkholm, because it's such a wonderful deconstruction of Epicness, and movies love Epicness. Of course, that's why it'd never get done, because it'd cost as much as an Epic movie without having a chance to bring in as much money.