Now I've been searching for an answer for this specific matter and since I can't find and official word and players can't test it themselves, I'm hoping I can finally get an answer here.

I've already bought a retail and a steam version separately from eachother and have become aware of a couple of scenarios which leave me confused about the state of the seeming one-way compatibility. Here's what I understand so far from reading around:
-A steam purchase of Heavensward cannot be used for a retail copy.
but also
-A retail copy can be used to log on steams trial version as a standard player
but as I also already understand
-A retail copy can't be used to take advantage of steams wallet function

I love the steam platform and would like to play on there, but if I can avoid rendering my retail copy useless I would like to have a go at it. So the question is:

Can the retail copy of Heavensward work on the Steam base game or does the block work both ways?

Or to pitch it differently, is it possible to make a single purchase of Heavensward that won't hinder one version of the base game in favour of the other?

Thank you.