New nipples all around and replaced four (out of 28) spokes with new ones; two were stuck in the nipples, one had a sharp bend and one a very obvious nick. Shifting the spokes over one by one did appeal but I ended up removing all spokes, putting them in four piles and then, after cleaning / checking, lacing them as I am used to.
Just cut through the old rim, there was 0.3mm of rimwall left... New rim is 25mm wide, the old one was 23mm at the brake track flaring to 26mm. First time I've worn out a rim, after "only" 22000km.