Yes a turbo uses exhaust gasses to compress air, but exhaust gasses are not compressed air...

Depends, Are you driving a Dodge???

I am with you on the efficiency point. I am just trying to think of how they would (could) manage this.

Yes lots more testing!

By doing so you now have additional electrical requirements, Automotive batteries are not the greatest devices for long term charges (without being complimented by an alternator, which is not doing anything when then engine is not running), so now we need to add additional battery(s) which results in additional weight.

Yes but the point being, pertaining to the original question, if you were to compare the hypothetical losses of rotational mass and direction change from a camshaft (of any style) to the losses of a compressors rotational mass, the compressor (hypothetically) would be more.

Very true, but like I said, the cam profile seems like the least of the worries in that equation.

But then does it not price itself out of most markets?

Yes and no. It comes around to reliability and maintenance. If the air compressor is much less reliable than a timing belt or chain, is it really an improvement?

This is defendant on the required average pressure. Most cars run <40 PSI for fuel. Maybe thats all this takes for the air, maybe it requires 100 PSI, thats more force on the line and will require stronger lines.

Yes, this is completely plausible, and a GOOD injector could handle either fuel, but that also drives up the price of the system, as does the fact that the engine would need to be built to withstand the higher temps. (this is why diesel engines are $7,000 - $8,000 add on options for trucks.

Sure, if 1 actuator goes, NBD. Point being (and I know this will happen because CVK is the man) the system needs more testing, reliability of the compressor becomes a huge deal. if you have a compressor that frequently breaks or needs frequent maintenance then the system voids its gains for most applications.

Yes, but not at such high rates of speed so frequently. Just making the point that there is more margin for error.

Understood fully, and I am in no way saying that the losses from a compressor outweigh the gains from this system. I am thinking more in terms of other losses (look at loss of space from batteries in electric cars). What if the compressor is designed to run on electricity rather than engine rotation (if your pump is…

I hear you, and like I said, I am all for improvements, but the idea of the camshaft has not changed in over 100 years. Sure manufacturing processes have, but the general idea of a solid rod with lobes that push valves as it rotates has not changed. If it were up to me, we would all still be driving cars with carbs…

Thats why you use timing chains...

While you are correct, I don't see this method as being as efficient for diesel, making the use of diesel virtually pointless. I could be wrong though.

It is quite plausible, as you can open and close the valves at a much higher rate of speed with more accuracy and it can be timed using crank position sensors.

Explain how exhaust could be used as a source for compressed air?

That is truly dependent on air requirements. And no, a compressor of virtually any size will have more rotational mass than a camshaft.