Marking issue as duplicate could subscribe its subscriber to the referenced issue

Description

If an user is subscribed to an issue, he most certainly is interested by the ongoing discussion about the topic. If the issue is then marked as duplicate, the issue is closed and discussions stop (and transfer to the referenced issue). However, the user subscribed to the duplicate stops receiving any notifications and has to manually track the topic.

Proposal

Wouldn't it be an idea to subscribe the user automatically to the referenced issue?

Links / references

Merge issues: gitlab-ce#26372
Subscriptions in general: gitlab-ce#26892

Overview

As I understand, 'subscriptions' is an ongoing topic that has not been finalised (see gitlab-ce#26892).