Can never understand people who so readily scream incest in step-sibling relationship. I mean you could have your current gf/bf become your step sibling the next day if your parents decide to marry, will your relationship be suddenly 'incest' then? Incest isn't even a social construct, it's genetics aka biological.
Contexts are important. If you're step siblings from childhood then yeah, getting together would probably feel super weird but if you're virtually strangers or were already in relationship before the 'step' initiation then it's whatever, it's literally just titles. Might be even a plus since you'd have done all the song and dance with your in-law already by then lols.