Exchange 2016 - Linked Mailboxes

I could not find a location to ask about exchange 2016, so asking here as it also relates somewhat to 2013.

We have 2008 functional level forest with Exchange 2013.  There is a trust to a 2003 functional level forest and users in that forest have linked mailboxes on the exchange 2013 server.

Now migrating to Exchange 2016.  I'm trying to find out if the users on the 2003 functional level domain will still work as linked mailboxes when upgrading to Exchange 2016.  Documentation on this scenario appears to be non-existent currently.  The 2003 forest is only an account forest, effectively using the 2008 forest as an exchange resource forest.

Thanks,

Matthew