well, it can go down to 640px Horizontal, but that will not Increase the Maximum Framerate. It will however allow you to increase the Record time, as the File-Size per Frame is smaller because less pixels, so it can fit more Frames in the Memory.
So it can still be useful, if you try to Record some Long Event or Process, and need the High Framerate.
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And, yes Sensors that can do that and even way higher performance ones are Available, but every bit better these get, they get MUCH more Expensive.
Also, the LUX2100 can do Plenty more than what the Chronos 2.1 Specs are, but the Electronics inside the Camera Limit what they can Pull from the Sensor.
Same as with the Sensor, that Electronic for Readout of the Data also gets very Expensive fast when it gets really high end.
In the 2.1 the Readout Electronics can keep up well enough with the Sensor for the Most part on the High Resolutions, but for the Really Fast Framerates that Sensor could handle in Theory, the Camera just cant read it fast enough from the Sensor, so it tops out.
The LUX2100 could apparently do 125,000 FPS @ 1920 x 8 (Full Sensor Width, 8px High), just the Problem is, Rest of the Camera is not able to keep up with that.
See:
luxima.com/product_briefs/LUX2100.html
forum.krontech.ca/index.php?topic=463.0
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There has been some Thread somewhere here, where Somebody from Krontech Posted instructions on How to Mod the Firmware, so you are able to Reduce the Resolution on the 1.4 so far, that you can get 100kfps on it, As it is not officially supported, and has pretty bad image Quality and is unstable.
Its Still not Clear, if something like this could also be Possible on the 2.1 (not quite that Extreme like on the 1.4 probably, but even 35kfps on the 2.1 would be a pretty big thing), but it seems like the 2.1 is much more Limited by the Hardware of the Camera on those high Framerates than the 1.4
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That being said, the LUX1310 the 1.4 uses is apparently able to do 1 Million "Frames" ( Lines) per Second, if used at Full Sensor width, but only 1 px High. So basically a Line-Scan Sensor.
luxima.com/product_briefs/LUX1310.html
How Realistic or Practicaly Possible it is to Reach that is a whole other story, just like on the 2.1, as you also need to read all of that Data off the Sensor fast enough, and not all of those chips needed for Readout of the Sensor like such weird or small Resolutions.