Hi.
I'm just a random Japanese Affinity user, but I have to say... I desperately need a vertical text feature for Japanese.
Currently, I have to do some tricks in order to write texts in vertical format. Inserting new lines between each character, rotating characters one by one, converting font... etc. Yes, vertical writing isn't impossible, however, it forces me to do such a hustle, and it also causes some problems. For instance, it's not easy to modify after entering texts.
Vertical text is crucial for Japanese language (and some other languages probably use it too), so it would be amazing if they add this feature. I mean, I totally agree with the OP.