What new developments did you find?

Hmmm, 4 views for your post in 1 hour. Perhaps one of the other three was encouraged to complete and post the latest updates in the wiki page (I'm watching it so I receive email notifs): https://wiki.scn.sap.com/wiki/x/IpvHGg

Seems like you've found the more significant updates already in your post ^^. Personally I don't necessarily agree with how some of the changes were implemented, or the level of completeness, simply because the silo effect is still too prevalent and tags are treated far to individually. The 'My Followed Tags' filter should be in all places: activity feed, blogs, answers, search results, etc. and not obscured only in answers. It should also be a multi-select checkbox list for establishing an SQL IN clause.

On the positive side: the activity stream/notifications are back... thank you!
I have somewhat mixed feelings about the latest improvements...
The activity stream/notifications look slightly more visually pleasing, I agree. Bold text and an obvious link for the primary tag? OK, makes sense and looks better.
But why do we need to see an additional secondary tag or a user tag there? In the case of blogs you can't show all of them (please, don't try to do that), so what is the point? Just get rid of this additional line, if I can't figure out what what a question/blog is about from the title, 2 lines of content and a primary tag, then a secondary tag and a user will not help. Not much of an improvement of getting a more compact Activity Stream, I am afraid.
And still, most of the horizontal screen estate is wasted for no logical reason. Can't you increase the width of the list, get rid of the useless secondary tag line, move the primary tag at the top - at the same level as the activity type ('posted an answer to question') is shown, change the relative time to an exact time-stamp (dd.mm hh:mm)? If you increase the maximum width to a reasonable value, the same content text can fit into a single line.
As a result, in total you can save 3 lines (initially 6), which results in almost 2 times less scrolling.
The filter for Activity type is taking too much space and is always collapsed. This is not very useful. I guess, it can be moved up and instead of the current form, to use something like the activity menu.
Here is an example how the site for my utility bills handles a similar scenario:

I am slightly disappointed, that I won't be able to take an advantage from the new filtering options for questions: I don't follow any tags and I am not planning to (thank you, I get enough updates already), but I wish to have an easy way to filter by tag (multiple select for tags, ad hoc). Why should navigation improvements be tied only to followed tags?

Release notes blog published today by Jerry:

https://blogs.sap.com/2017/01/25/release-highlights-as-of-january-23-2017/

Hello Juergen,

I am sure the release notes will be updated and there will be further announcements made. Glad you like the new features that were rolled out! I believe the feature of automatically marking a notification as read when a link in the notification is clicked was also rolled out. In addition to the white space removal from the activities and Notifications, there were a couple of other minor adjustments to the UI: the text description for each activity was decreased to two sentences. The primary tag text was brought up to right under the content title in activities as well for UI consistency.

I also think there was a new feature added to discussions in the archive that allows users to "view more" on the given topic.

Still no fix for a major bug reported in November?! You gotta be kidding me...

I have not noticed any changes. Never go to the whole Q&A list, so would not see the filter if it wasn't for this post. And I agree that this would be more meaningful if the same functionality existed across the whole site.

"Support Services" tag has already been available for a while, not sure why this is just being announced.

"Header navigation update (SOC-4681)" - no idea what it means.

Change in the activity stream is barely noticeable. It just became 5% less atrocious.

Don't mean to rain on anyone's parade but with so many bugs reported and so many ideas posted I believe the community deserves more significant improvements. People will start dropping like flies if the pace of changes continues.

To my mind using "My Followed Tag" filter I will be able to see questions with multiple followed tags on the same page... Unfortunately not, it's just a collection of followed tags links.