Following on form the Bank tagging idea I wonder inf there is a way of importing this into a trade account system as I can log in and view invoices online through the company I have a trade account with it would be useful to be able to some how pull this invoice across into quick books rather than manually entering each one as I currently do. May be these more advanced things could be bolt on pay for things to cover your time and investment eg £20-£40 a year for example.
If this is more of a unique feature (for example, not many people would require it), t may be worth investigating the API. It’s easy to use, all you need is a bit of coding knowledge. If you don’t have that - drop me a PM, I’m more than happy to help. 
In general we tend to avoid any specialist integrations unless it is likely to benefit a large proportion of the user-base.
There are infinite business cases for sharing accounting data with CMS, stock control and order procurement systems and each one would take possibly weeks to develop and test.
As @Parker1090 mentions for any kind of bespoke integrations you’d be best off looking at the API.