There are new materials and lubricants, etc. However, the few that are practical are, or have been, exploited in current systems. New technologies such as composites and ceramics exist but applications in high pressure compressors are few and far between because they either have the wrong expansion characteristic, wrong wear patterns, heat sensitivity, cost, heat dissipation, etc. Compressors that are 50 years old, obtained from the military are still in use today. Let's take a look at what they were made of; Materials used in these machines include magnesium blocks, aluminum bronze connecting rods, heat treated stainless steel crankshafts, stainless valves and springs, heat treated inconel pistons, various aluminum and copper parts, brass heads, aluminum heads, heat treated steel barrels, teflon and butyl seals, copper seals, stainless bolts, brass gears, and so forth. All that is in one compressor block which weighs 15 pounds and has a real output of 4.2 cfm at pressures well above 3000 psi. I've seen these operated at 8000 psi for test purposes.
There is no free lunch. The energy required to fill a SCUBA tank is fixed by the law of physics. All compressors, regardless of size, are about 90% efficient and cost of ownership would not be appreciably affected by scaling down. A smaller compressor which is also smaller in output capacity could employ less material by weight and lower cost materials but the main cost of the compressor is tooling, labor, marketing, liability and other non tangibles. Some costs can be made up on volume and cheaper materials which can survive slower rotational speeds only. However, mass production could never be there because nobody would want the mini compressor. Most of this cost of production has already been resolved for the commercial market. It was accomplished by economies inherent in the production process, not alternative materials except where cheaper, less durable materials can be included. In other words, production tolerances, production processes and unit volume are factored into a cheaper machine. That is why one can buy a Coltri or Alkin for 3 grand as opposed to 20 thousand(in today's money) for the small military compressor described above. The commercial units weigh a lot more and cost a lot less.
There is no technology which can scale down these machines without exorbitant cost, even should output be reduced because one is dealing with high pressure air/gas. Compressors are not like watches, there is no disruptive technology such as a micro chip which can reduce the size and cost. In a very small compressor, all the moving parts would be there, just smaller. Such things as the Wankel engine have been tried in the automotive world. This engine is very compact, simpler and powerful but the need to control high pressure gasses is a problem that required untold hours of (expensive) engineering time with questionable results. That is to say that efficiency of the Wankel never really over took the reciprocating engine regardless of the level of sophistication used in the chamber and gas seals.
Most of this has been explicitly stated or implied in the above posts already so this is just a courtesy which puts some emphasis on what has already been explained.
