Might an option be added to the banker's dialogue to get your account balance?

It is there. Although there's no dialog tree for it - you hear it automatically, which isn't always a good thing ( Others around you hear it)

I mean a dialogue option to ask it - not using a workaround.

Aekula It is there. Although there's no dialog tree for it - you hear it automatically, which isn't always a good thing ( Others around you hear it)

As part of their design, a lot of the script-based task conversations (tailoring, banking, scribing) are only heard by the speaker, to avoid being horribly spammy for others nearby.

It should be easy enough to add a dialogue option asking for the balance.