In what ember-source version do I no longer need this addon?

[NullVoxPopuli]

I forget if this has been implemented yet

[chancancode]

From the README

This addon provides a polyfill high fidelity reference implementation of
RFC #389, including the proposed
amendments in RFC PR #620.

Please note that while RFC #389
has been approved, it has not been implemented in Ember.js yet. As such, the
feature is still subject to change based on implementation feedback.

When this feature is implemented in Ember.js, we will release a 1.0 version of
this addon as a true polyfill for the feature, allowing the feature to be used
on older Ember.js versions and be completely inert on newer versions where the
official implementation is available.

I believe this is still current.

[NullVoxPopuli]

how do we implement the element helper? would that be a glimmer-vm thing?

[chancancode]

Yeah. I think so. We will probably have to invent some new concepts in the glimmer-vm internals to thread this through. I suppose we can also try to reuse the existing code that handles the classic ember components since apparently that works almost perfectly fine.