I built and tested the latest m.relates_to branches and hosted it on https://lant.uk/riot/new_replies
Things I tested:

In conclusion, for the most part it's great and nothing was show-stoppingly broken, but the ⚠️s represent tests where the outcome could have been a little bit better (mostly from a UX perspective).

I have just been giving this a little test a couple of quick thoughts:
there seems to be no way to click the rendered reply to jump back in the timeline to the location of the original message (to get extra context etc). Where as there is only this on /app currently, it would be nice if the (body of the) reply was clickable to jump back in the timeline imo.
When the in reply to of a reply to a reply is collapsed, the user pill is not clickable, either to take you to that user or to expand the reply. (I was expecting the latter)
Finally, I can't quite put my finger on what it is, but I feel that chains of two+ replies get's a little unclear. It's not visually obvious to me that I am effectively viewing a thread.
forgot to say in the original comment, but this looks awesome and I can't wait to have it!
message rendered to the timeline as a message
is VERY weird
oh I see why its happening, the local-echo does not include the m.relates_to because it gets stripped off to be put on the envelope event, so the local-echo needs to copy it accross
I've stuck bug p1 major on this because all these minor snags being addressed added up to a major improvement on the replies UX
2. of @Cadair 's thoughts has broken out into https://github.com/vector-im/riot-web/issues/6670
Not sure if the design is up for consideration as well, however I'm kinda a fan of this:

It feels like it takes up a lot less space, despite only saving a line or two.
ironically i think that matches @jounih’s proposed design in the rework
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Matthew Hodgson
Matrix.org
On 10 Jun 2018, at 02:40, Travis Ralston notifications@github.com wrote:
Not sure if the design is up for consideration as well, however I'm kinda a fan of this:
It feels like it takes up a lot less space, despite only saving a line or two.
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When replying to a /me, the sent time is displayed on top of the avatar 
I'd like the ability to remove user avatars from replies in order to make them much more compact. Any other way of reducing screen space bloat would be appreciated.
Thank you.
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I'd like the ability to remove user avatars from replies in order to make them much more compact. Any other way of reducing screen space bloat would be appreciated.
Thank you.