Join extension attributes are not added to Order results (REST api)

[Bbbrinks]

Preconditions

1. Magento 2.1.3
2. PHP 7.0.8-0ubuntu0.16.04.3

Steps to reproduce

1. Define a Extension attribute for the OrderInterface with a join table:

    <extension_attributes for="Magento\Sales\Api\Data\OrderInterface">
        <attribute code="some_id" type="string">
            <join reference_table="SOMETABLE" join_on_field="quote_id" reference_field="quote_id">
                <field>some_id</field>
            </join>
        </attribute>
    </extension_attributes>

2. Make sure there's matching data in the SOMETABLE table and the sales_order table
3. Request orders via REST

Expected result

1. I expected to see some_id in the resulting json response (this does work for Quote extension attributes).

Actual result

1. No some_id in the extension attributes property of the json response

[Bbbrinks]

As far as I can see there's a missing call in /magento/module-sales/Model/OrderRepository.php:

$this->extensionAttributesJoinProcessor->process($this->quoteCollection);

The //magento/module-quote/Model/QuoteRepository.php does have this call.

[PaulBoss]

Is there any update on this?