The SD channels are here to stay until they come up with a way to replace all those SD only boxes, but there doesn't seem to be any desire to do that
Thanks, I never realised this was happening on 19.2°E! Is there a name for this system? I'd happily sacrifice the picture quality of regional news if it meant everything else was improved.
I'm not sure of the name, but technically it works by the service IDs for each regional service in the MPEG-TS tables pointing to the same VPIDs/APIDs as each other most of the time, and then during regional content dynamically updating to point at separate PIDs as necessary. Most receivers show the content of the PIDs as told to them by the service information, so take into account any live updating.
Here's an example of it on the new-ish WDR HD transponder on 19.2°E (11523H) -
DVBS DVBS2 DVBS2X Bitrate Monitoring 11523 H Astra 19.2East
As you can see in the bitrate graph, most of the time there is just one ~15Mbps video stream shared by all WDR HDs, but then during "Lokalzeit" it splits into 11 separate streams. Köln is the "master" stream so it keeps the same PIDs throughout, whereas for the other services their PIDs dynamically change.
You can see this in action if you watch one of the WDR HDs (other than Köln) at 6:30pm UK time, including today. On most receivers it's a pretty seamless switch, sometimes a second of glitch or so. You may of course notice the picture quality go a bit soft because of the lower bitrate, but as you say - it's much preferable to have lower regional news PQ as a trade-off for better general quality for 23 hours of the day.
The same applies for most of the other German regionals (NDR, MDR, RBB, BR), as well as for those handful of SD RTL/Sat.1 opts (RTL HB NDS, Sat.1 Bayern etc)