... even when the device used to achieve timeline divergence didn't involve time travel and similar.
Yes. As per my reasoning on another thread, all SF (what if?) is on-topic, including alternate history.
(To put this thread in context, it was written at a time when the site was wavering between being limited to science fiction, or being about speculative fiction in general. Eventually we decided that this site was about speculative fiction in general — the name of the site is “science fiction & fantasy” because these are the most recognizable subgenres of SF.)