I remember the blogrolls that Dave talks about, I had one on my original blogs too. Question: what is the purpose of a blogroll? Is it advertising of other blogs you read or is it a list of links (bookmarks) from which one goes to read other blogs?
For me, I used my blogroll as a bookmarks list, but that has been replaced by RSS. Today, I don't open blog web sites to read, I browse through my news river and share links of items I want to read to Radio3. I added a step to the process Dave describes where I have an IFTTT applet that adds items that I add to my Radio3 linkblog to Instapaper and Pocket for later reading.
Basically, my RSS subscription list is my blogroll.
In regards to the question of how to monitor a particular blogging topic, like IndieWeb or say 1999 blogs, that can be done with a topic-specific River. As an example, back when 1999.io was new and getting attention, Andy Sylvester created a 1999 river from feeds created just by blogs written on in 1999. Sadly, it looks like may one of the only 1999 bloggers left.
The missing item would be a way from the topic specific river to get a page of the sites that part of the river subscription list.
FM, I continue with 1999.io, even have a server on AWS, but it is a lonely venture. Dave seems to scatter a bunch of stuff without enough focus to fully develop anything. That's OK (the price is right!) but sure doesn't exude permanence.