EDIT: After reading through the Git issue and the other comments in this thread, it is not very clear to me what "combining comments from cross-posts on the post screen" means. I understood it at first to mean that you will pool all comments together and show all of them in all cross-posts, but now I am not so sure. Still, in general terms, I think that mechanisms to share activity with niche communities are good
I would say yes, there are cases in which I have thought that this would be a nice thing to have. Especially when cross-posting to a smaller niche community.
I can think of a few potential small issues. For example, cross-posters can edit the body of the message, so you might in some cases end up with comments that seem out of place as they refer to the content specific to a cross-post. You also have the rare case in which the same post might mean different things in different communities.
But, overall, I see it as beneficial. Quirks can be fine-tuned later on.

I like the idea of PeerTube, but I tried running an instance and was unable to sustain the experiment for too long. I made it very open and it got quickly flooded by pirated TV series and spammy and heavy content.
After that, I had a difficult time at some point finding an instance to host some videos I wanted to upload - and, having had that failed experiment before hand, I can see why the instances that do survive are often those with more stringent filters and less generous with resources.
So, I am sorry to "chime in about the shortcomings", but hosting a PeerTube instance can be a demotivating experience. You set up the infrastructure expecting to contribute to a space reminiscent of the old youtube, and you see it filled with spam. The signal-to-noise ratio is just awful and it is expensive. To avoid this, you can be an aggressive gate keeper - but this makes the platform less friendly to people who are looking to find a space to share their original content. Gate keeping is also an additional effort that you need to make. In the end I chose to just shut it off as it was more of a hassle than fun. By comparison, hosting a Lemmy instance is fun, much much cheaper, and little hassle.
I still haven't given up on the idea of Peertube, though... I have some video ideas, and when I finally get to making them I plan to make another instance to host only my channel. Then, I would be able to host my own channel using my own infrastructure via a federated network. This use case would work very well for me, and it can probably work for many others. So that is one way of building the Peertube network.
General permissive video uploads is something that makes YouTube such a powerful platform though, and that is very difficult to replicate.