Just in case you missed the crucial bit:
"It won't offer any live content or replays."
So you'll still need the Discovery+ app to view live.
Don't worry, I get it.
You still need an active subscription to watch TNT Sports. Not that it's an issue for me as I'm locked into the service via a number of ways and currently have no intention of leaving in the near future.
There's currently so much content on the BT Sport app such as highlights on stuff I've not seen or would like to watch again. I'm just hoping that whoever is responsible for the upkeep of the new app allows a similar amount of content to be archived for a similar length of time. If not I will just have to accept it as it is.
Timeline technology as you call it is very much supported by Discovery+ including while casting. Actually the latter may depend on your Chromecast dongle or device as my (latest version) dongle has the Discovery+ app installed on it so no need to to cast from my phone.
@gomezz Bully for you. Like many users i am finding the discovery+ app temporamental at the best of times - as evidenced by similar feedback recorded by users on Play Store. As for casting, it doesn't seem to matter which method I use (whether i use my Chromecast Ultra device or a TV/PVR with inbuilt Chromecast). The result is still the same in that the app does not allow you to watch from the beginning when casting. This could be an incompatibility issue with the Google Home app itself, but somehow i doubt it.
As I post I am chase-playing the baseball currently being shown live on TNT Sports 1 using the Discovery+ app on my Chromecast dongle. So I stick with my assertion that it is possible on some devices if not on others.
Or have I been misdirected as to what is meant by "Timeline" in this context?
As to why some users have problems streaming with Discovery+ while I do not then maybe one factor may be that I tend to use it to catch up on superbike coverage midweek rather than pile in on a popular event live which would point the finger at the load on the servers causing it to creak?