If you have a directional antenna and you can rotate it, then yes you can determine the angle between two devices with a rough estimate of distance based on RSSI.
As far as time of flight, you need a clock that operates in the GHz range, and Flutter only uses a 40MHz clock. You also need custom analog electronics on the RF front end to do some tricky stuff with the radio wave as it hits the antenna. It's basically very complex to do TOF measurements on a platform like this. If you operate in the 5.8GHz range or above it's not too bad, and some chips are now being made available that support this. But 915MHz is very low frequency for TOF measurement, so Flutter's radio system simply isn't well cut out for this. I am interested in a module that attaches to Flutter and adds TOF capability but it would be a completely separate radio system operating in a higher frequency band. Positioning is important to Flutter's future goals, but I still haven't pinned down how we will do it.
Rotating an antenna should work pretty well though for angle. You should also be able to rotate a baffle around a Flutter board, but I haven't tested this.