Anonymous checkout fails with PDOException when profile has required fields

I found another old thread that describe parts of this issue, but not all of it, and it was marked as fixed because the original poster worked around the issue.

I'd like to strongly argue that this issue is NOT FIXED.

As it is now, if you add a new REQUIRED field to the profile, without then dinking around in the rule configuration, the checkout explodes in spectacular fashion with a PDOException error.

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key 'name': INSERT INTO {users} (uid, created) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1); Array ( [:db_insert_placeholder_0] => 3 [:db_insert_placeholder_1] => 1435681008 ) in drupal_write_record() (line 7316 of /...../includes/common.inc).

Here is the solution suggested in Account creation fails upon checkout, which I'm going to argue is a workaround, not a solution.

Go to admin/config/workflow/rules.
Edit the "Create a new account for an anonymous order" rule.
Edit the "Create a new entity" action.
Add something (ANYTHING) into the required field you just added.
Ideally you would enter a data selector to provide a useful default value from the commerce order.
Repeat for the "Create a new account for an anonymous order (HTML)" rule if you have one.

Why is this not a solution? Because simply adding a new, required, profile field IMMEDIATELY breaks your checkout, and you won't discover this until someone is ready to complete their order. The error occurs AFTER entering their credit card information.
"Potential for loss of sale" is an understatement.

Here are some things I've tested to determine what conditions the error occurs:
* Profile Field Required, Not captured in checkout: FAIL
* Profile Field Required, Asked for but not required in checkout: FAIL
* Profile Field Required, Required and captured in checkout: FAIL!!
* Reducing weight of the "Update the User with input from User Profile Pane" rule to 1 (so it fires before user account creation): FAIL
* Adding a Default value to the profile field configuration: defaults the field in the checkout pane, but STILL FAILS
* Tried multiple data selectors in the rule field configuration, all of which failed, probably because they reference the user account which does not yet exist.
-- "commerce-order:commerce-customer-billing:user:field-MYFIELDNAME"
-- "commerce-order:owner:field-MYFIELDNAME"

It looks like the ONLY remaining solution is to put something, ANYTHING into those rule fields, to allow the user account to be created.
The "Update the User with input from User Profile Pane" rule fires later and actually does the data copying, so it doesn't matter a whole lot what the data selectors are in "Create a new account for an anonymous order"->"Create a new entity".

I propose the following:
* If any default is set for a profile field, use that in the rule default data value, so that even if it's not shown in checkout, it'll still be saved to the user.
* If no default is set, use a "0", which should work for integer and text fields. It may not work for images, node references, or other more exotic required fields with weird validation, but it'll prevent most errors and hopefully keep checkouts from bombing.
* At minimum, if the above is somehow not possible, provide an unavoidable warning on the profile field edit pages with instructions on how to default these rule values.

I had a look at some of the rules definition files, but can't figure out where it's adding the profile fields into the rule config.
Considering I've spent an entire day trying to track this issue down and solve it for good, please give it some thought.
This issue can easily, silently, completely, disable an e-commerce site.