Tagify use for 4.x version : sending a pm to a specific user

Problem/Motivation

In the 4.0.0-alpha4, I took the maintainers' suggestion to use the tagify module to display a better looking widget.
As far as I know, to do that I have to select the tagify widget in the entity reference field widget configuration.
It's working great except for this : when you send a private message from a link with the recipient in the url, it no longer autofills the default value of the widget, as PrivateMessageThreadMemberWidget does.

Steps to reproduce

1. Install the tagify module.
2. Configure the entity reference field "member(s)" to use the Tagify widget.
3. Click on a link to send a private message to a specific user. The url should be : /private-message/create?recipient=XXXX. X being the recipient uid.
4. The member field is not filled with the recipient's name

Proposed resolution

Find a way to fill the value with whatever widget is used, I guess ?
Maybe it's not intended to work with another widget than the default one, but maybe it would be useful to extend the tagify widget to provide this private_message functionality.
I can work on some code for this, but would like to have the maintainers advice on the more compliant way to do this for private_message without adding external dependencies (maybe a tagify submodule ?)

Side notes :
- I was surprised to see that in the 3.7 version update, the widget is now a standard reference field too. Wasn't this change supposed to happen only in the 4.x version ?
- Thank you for maintaining this module, it has been a core part of our social network from the start !