You are actually the first one asking about that feature 😄, I guess touch devices made this capability less relevant. Not really planning to resuscitate it for the moment, first finalising the refactoring process before adding new features.
+1 for col resizer.
FYI We're looking at working around this at the moment by popping our table filter tables into a bootstrap panel and using lobipanel (http://lobianijs.com/site/lobipanel#examples) to allow us to pop the table (and panel) out of our fixed width layout site so it can use the full screen. Its not exactly the same effect but its better than using a lot of scrolling using grid