I've been a TotalFinder user since 2012 and it has never disappointed me so far. I'll be very happy as long as support for the current feature set is continued on future OS X releases, and I'm personally fine with disabling part of SIP. (Yes, I fully understand the tremendous difficulty of working with private APIs, monkey patching and stuff, and I fully understand sometimes breaking changes simply make certain things impossible. Cheers to you guys who have made it happen then kept it working over the years.) It's awesome to have a new developer with equal passion for TotalFinder.
Rather than suggesting a new feature, the only minor annoyance for me in TotalFinder at the moment is the following: I have chosen to "automatically adjust widths in Column View" (one of the most important reasons I use TF), and limit maximum column width to 400px. Occasionally I would have some long filenames that exceed 400px, and they'll be truncated; in this case I could double click the column divider (Right Size This Column) to show them in full. In stock Finder, this change would be retained until I navigate away from the resized directory. However, in recent versions of TF (ever since automatic resizing was fixed for El Cap, currently 1.7.12), the column will be resized to 400px every time the selection changes, even within the same directory. Presumably this is a side effect of the automatic resizing fix — the view seems to be refreshed (with widths recalculated) for all navigation moves.
The aforementioned problem happens rarely enough because I seldom have filenames that long. I probably should have reported a bug, but I never remembered to do so