I would like to propose a form in which records in two (or more) tables can be created at the same time. For example I have a relationship "Contact has one or more Addresses".
Using the current system I have to - create the contact - go to the sub tab - add a new Address
I can work around this by having fields on the Contact form which collect the Address data and then create the Address record by trigger. This works but it means I have to build and maintain any validation rules twice. It also means that any reference from Address (e.g country) have to be duplicated in Contact, just for the purpose of creating the Address.
Another workaround with the new Navigation buttons would be to trigger the presentation of a NEW Address form immediately after saving the Contact. For the user this is a two step process and he is "forced" down that road even if he does not want to add an address.
So my suggestion is that it is made possible to embed a NEW Address form in the NEW Contact form.
Other examples: Invoice and first invoice line Project and first deliverable etc