I have been thinking about this myself for quite some time ,for similar reason as @clive , you need to split the transactions and it would be handy if Bank Rules can accommodate this.
eg Split drawing / Business use as mentioned
eg split non GST component / GSt Component - Phone telco if you have a mobile repayment on plan then that part is usually GST free and shouldn’t change each bill
eg rego on vehicles have non GST/ GSt split usually
These are some example when handy to have split on bank rule but as in all things, the down side of having split in bank rule is that non GST component can change each bill / renewal so one would need to edit the bank rule before recording .
This may be in part why @lubos has not implemented to date as mistakes can happen easily .
however for entries that never change eg I have a client that claims a pro-rata on rent paid as his unit is his place of business being a computer repair man and has a room strictly setup as his workshop with permission from Owner,… that split would be good to have as a bank rule as it happens weekly. The tracking code addition would be a great idea as well.
If coding to facilitate this modification to bank rules would slow the overall functionality of manager then I would not be in favor of implementing as it just means a bit more effort and attention is required by us at time of doing entry and bank recs
but still well worth considering as the program continuities to evolve for the better .