I think a “retro” tag would help indicate projects that use older technology for the sake of using that older technology. There’s definitely a separation between just more historical posts and say, the series of articles on the 8088 MPH demos (1 2).
I almost always learn from the hacks that people have accomplished on older hardware or the problems they encounter in those kinds of projects, rather than just a paper on that technology design (from the time period) or a description on it’s history (not that those aren’t valuable).
One of the 8088 MPH stories: http://www.reenigne.org/blog/1k-colours-on-cga-how-its-done/
Writing an OS… in QuickBasic: http://back2basic.phatcode.net/?Issue_%231:Writing_an_Operating_System..._in_QuickBasic