I’m assuming that many here are long aware, but to those looking around here because they’re currently-installed version of RT cannot deal with their Raw files, or considering whether they’d taking a risk by buying an S5II:
libraw has added support for the new format (though apparently not in any finished release), and while I have not seen a definite announcement to this end, Simone Gotti has apparently finished what he said he’d do in March, and the corresponding issue was closed on 2nd of June.
I just installed the latest version off Git (rawtherapee-git, installed via AUR, on Manjaro).
It opens the Raw files from my S5II, and they look good.
Finally! Big thank you to everyone involved!