The reason this does not exist as a simple negative value for the speed property is because reversed clips do not play and seek reliably. Why? Because of many challenging, temporally compressed formats that have long GOPs and/or B frames. Therefore, this feature needs to be put into a special place like the Properties overflow menu where it will generate a new file that you can then use. It is doable after deciding on a particular format or giving a choice of formats. I lean towards some lossless format like FFV1, but I just know someone is going to put a 2 hour video through it and complain about how big the new file is. Also, do I need to ensure every audio, text track, and bit of metadata of the input file is preserved through that process? When you face decisions like this, there is a plethora of other things to do and such little time; delays are inevitable.