MarkoH01: Just opened a support ticket and told GOG that I either want an ETA for the classics or a full refund for both games. Since they simply did not deliver what was part of the deal I am quite sure refund won't be much of a problem.
If you did not download the game you can simply withdraw from purchase within 30 days.
Correct. I bought both Bioshock's on launch day (17th Dec) but later had a strong feeling
"at a later time" would end up like their Remaster bugfixes (people still waiting over a year, even on Steam). I deliberately didn't download either remaster whilst waiting, then applied for a refund for both games and got it through very quickly. I'll rebuy only if and when the Classic versions are added.
If you haven't downloaded the Remasters you're virtually guaranteed a refund within 30 days (Wed 16th Jan for those who bought on 17th Dec launch day). If you leave it later than 30 days though, there is absolutely zero guarantee you'll get a refund simply because the promised Classic versions are both classed as "bonus material" and not the 'main' game being sold. Whether GOG gives an optional post-30 day refund if the Classics never materialize remains to be seen, but it's certainly not guaranteed and a gamble for those who want to try and wait it out.