if you have an existing post that you want to show in a different channel, you can edit the message and cross-post. This will add the top-level post to the different channel, but will not include the full set of replies. We will keep this request in mind as we evolve the cross-posting feature in the future and update if the status changes.
Details on cross posting can be found here: https://support.office.com/article/cross-post-a-channel-conversation-in-teams-9c1252a3-67ef-498e-a7c1-dd7147b3d295.
Thank you for your continued feedback, we have addressed #1 in the list above. Contextual search within a specific chat or channel is now available. To learn more, please visit https://support.microsoft.com/office/search-for-messages-and-more-in-teams-4a351520-33f4-42ab-a5ee-5fc0ab88b263.
The feature team continues to make progress on these asks, and we will share an update when one is available.