I think you’re flogging a dying horse, for a couple of reasons:
The “precise aspects of ITD” are far more complex than a simple static delay time time, as discussed it varies by freq but also, it has to be integrated with other factors, such as ILD obviously but also with the quite complex and variable freq response created by skull and pinnae diffraction and absorption. If you don’t do this, FR and ITD effectively fight with each other and can cancel each other out. Experiments show that a sound which should appear to be panned say hard left according to it’s ITD, will be perceived by some/many to be centrally panned if the skull/pinnae FR for a hard right panned sound is also applied. So if you ignore this or implement it with some simple static value, the results will be unpredictable from listener to listener and you’ll have done a lot of work but be back where you started. And, if you implement it correctly, then it’s no longer a crossfeed plug-in, it’s a HRTF plug-in!
However, HRTFs have a serious problem. While the processing power in mobile devices is now sufficient to cope with implementing them, the problem remains that generic HRTFs don’t work well for a lot of people and getting usable personalised HRTFs is very far from practical for consumers. However, there seems to be considerable research going on in this area. For example, there’s a published paper which uses simple skull measurements with a tape measure, correlates them with a database of HRTFs to come up with a function to modify a generic HRTF and thereby personalise it to a significant degree. However, I suspect most of the ongoing research isn’t being published because it’s being done in/by the corporate world. Apple filed a patent for using ear scans created by the iPhone’s “true depth” camera to personalise generic HRTFs. Dolby recently allowed personalised HRTFs to be used in their Atmos RMU (for content creators), implying something in the pipeline for consumers down the road. I would think that if Apple (and probably Dolby) are working on this, Google and some other big guns probably are too. So, I think we’ll see a lot more products incorporating HRTF/“spatial audio” functionality and incremental improvements to this generic HRTF problem, probably starting in the fairly near future.
G