You can submit that as a feature request to support@airtable.com.

In the meantime, you can get that feature with linked record fields. It will sort the linked records that the user can choose from by mirroring the sort order of your topmost view in the linked table.

Hope this helps!

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You can find something similar to that by using a linked record field (rather than multiselect), allowing linking to multiple records, and having a lookup of the ñame of such linked records sorting alphabetically. 
 

I’ll share more on this tomorrow!

If you have a paid plan and have access to Extensions, Batch Update can accomplish this without much issue. Just configure your batch update settings like so:

Just tested it myself and it should do the trick! 

(Fairly certain you can also use Batch Update to sort Linked Record fields in the same way.)