I find it useful to be able to toggle whether an item is selected by middle-clicking on it (with RISC OS, right/Adjust-clicking) and to be able to use the same button to drag a box which inverts the selection status of enclosed items. (It's actually one of the first things that I tried when I first looked at Thunar.)
Created attachment 650 Implement middle-button toggle and (optionally) drag box
I think the 'toggle on middle click' feature can be committed (tho, the details view is missing from your patch). But the 'rubberband selection on middle button press' does not look like a sane feature for Thunar, esp. since it conflicts with the mouse gesture and would thereby introduce another option.
Conflicting with mouse gestures isn't a problem. I tend to either ignore their presence or disable them anyway...
Well, as said that would require another option. We already have too many options. Thunar should stay simple, with sane defaults. The "toggle rubberband selection" is already available via Ctrl+Rubberband, which is consistent with other applications.
Uhm, thinking about this again, even "toggle on middle-click" will be confusing, esp. in single click mode.
Moving to 0.4.0rc1.
Hm, no, I don't think it makes sense for Thunar.
Resolving to WONTFIX.