It sounds like you are expecting something like QuickBooks Desktop functionality from QuickBooks Online - which I seriously doubt you'll ever get.
Desktop can include up to 15 item custom fields on invoice tables as 30 customer custom fields in the header of invoices and every other sales transaction - and for good reason: It's what customers want.
It seems easy enough for QuickBooks Online to copy Desktop, but for 25 years they haven't bothered. I really don't think entering another suggestion will make a difference.
