Not all things that look like "interpolators" need traditional lookforward lag.
Mice and head trackers can already run at 1000 Hz. It's the GPU that cannot keep up.
Instead of black-box interpolators (e.g. Sony MotionFlow), a smart interpolator can be made to know the high-frequency controller inputs in realtime, and doesn't even need to use guesswork-based interpolation for everything.
Just shift everything around based on the high-refresh 1000Hz controller input. (In other words, "reprojection").
Also, knowing more data about the source (e.g. near-zero-lag controller input stream) eliminates lots of interpolation guesswork. It's much like how H.264 (video compression) is heavily interpolation-based mathematics during the video codec, but it had full awareness of the source video material, to successfully compress it virtually artifact-free.
So basically, you are simply giving a smart interpolator full awareness of things like geometry & input at a higher rate than the GPU renders. To avoid guesswork on those kinds of items.
Things like future multilayer Z-buffers can help solve a lot of parallax-reveal problems of trying to create intermediate frames, and there are future tweaks they are working on to eliminate reprojection artifacts. Like artifacts or reprojection distortions around edges of objects in front of objects. So adding intermediate frames with full parallax effects can eventually become artifact free because of the GPU's knowledge-in-advance of what-behind-what. Basically, more advanced reprojection algorithms that can create near-flawless intermediate GPU frames (without lookforward) without a full polygonal rerender.
Prediction helps (as it does for Oculus), but remember, we have controllers that already go at ultra high frequencies, and it is expected headtrackers will eventually become ultra high frequency too -- and that extra data can reduce the need to do lookforward prediction.
It's all very complex, with many researchers working on multiple solutions, but it can reduce the average processing-power-required per extra frame, and it can theoretically allow high reprojection ratios without lookforward lag (e.g. theoretical future 10:1, such as multiplying 100fps to 1000fps, at least with 1000Hz input devices like 1000Hz gaming mice, and 1000Hz head trackers).
Several VR scientists have indeed advocated the need for 1000Hz eventually, someday in humankind, as there are confirmed tangible immersion benefits to getting that high and beyond.
That's why I wrote that article full of motion demos explaining the visual science concepts of why 1000Hz displays are needed. It will be useful for passing a theoretical future Holodeck Turing Test (not telling apart a VR headset versus transparent ski goggles in a reality-versus-VR blind test), in terms of Morarity-style or Matrix-style "it's real" VR.
Many tricks layers upon each other, to achieve what's being achieved today, and this creativity will only continue. Lagless lookbehind-only interpolation (utilizing ultra-high-Hz controller input to reproject new 3D position). Foveated rendering too, yes. Realtime beamtracing with realtime denoising (NVIDIA scientist paper), perhaps. Maybe even all piled on top of each other simultaneously, perhaps.