Hi guys,
I believe Joe's first point references an issue that arose with the introduction of 4.3 where a contribution is initially recorded with no payment instrument results in "unbalanced transactions" - I searched around quite a bit and couldn't find any original tickets that explain why the payment instrument is required, but I found a few tickets from Sarah related to the fixes applied for the issue:
https://issues.civicrm.org/jira/browse/CRM-16548
https://issues.civicrm.org/jira/browse/CRM-13420
I am concerned that the requested change will cause a regression of the original issue.
I disagree with the second point in the initial description that states "When Contribution Status is changed to Pending or Failed, Payment Received should be set to null on screen" - I'm not sure what the use case is for changing a completed contribution to a status of pending, but for failed contributions (specifically check/ACH contributions), there could be quite a difference between the original receive date and the failure date (i.e. once verification is received or the check is returned) - the original contribution may have already been batched and would correspond to a possible deposit that is later returned on a bank statement (e.g. in the form of a negative amount due to insufficient funds on the payer side), so both the original receive date and the actual failure date are both valuable pieces of information that should be preserved.
In regards to the third point of "If Payment Received is null, and Contribution Status is changed to a value other than Pending or Failed, Payment Received should be defaulted to now.", I am not sure how this is different from the current default of "now" in the case of a new contribution, but in the case of an existing contribution, the same logic as explained above applies, and one could also argue that enabling the option to change certain aspects of an existing contribution, especially one that has already been batched, is against accounting best practices (but now I am going off on a tangent), but other issues reported with financial items could be exacerbated by these additional changes if allowed (e.g. https://issues.civicrm.org/jira/browse/CRM-18179).
Hope this helps when making a final decision,
Tamar
Submitted PR at https://github.com/civicrm/civicrm-core/pull/8469