Shipping Address Book
This fits under several categories, and applies to both mobile and browser-based QBO interfaces. The idea is for QBO in all its forms (browser, mobile, whatever) to provide an "existing or new" interface for shipping addresses wherever they are used (sales orders, invoices, estimates, etc) that can pull from either a customer-specific list of shipping addresses and/or a global set of known shipping addresses.
My company is an entertainment production services company. The "shipping address" represents the venue where services are provided. There is a many-to-many relationship between customers and venues. Many different customers may perform at the same venue, or certain customers may perform frequently at certain venues. Having a database of known venue addresses ("shipping addresses"), instead of having to type in the address manually every single time (and only being able to do so in the browser interface, and not on mobile, as of the time of this writing), would be a significant advantage.