Hi Dipen,
A couple of things to remember is that not all oils are full of additaves that get used up. I will speak in generalities here but for my industry I rarely condemn an oil because the additave package has been depleated to the point where it has to be replaced. Since we implemented oil changes based on condition (condition based maintenance) several years ago. We have had some applications that have lasted for 5+ years without an oil change. Our oils are normally changed out because of contamination ingress or generation, some contaminents are not easily filtered out. Rarely do we change the oil because of oxidation by-products the real selling attribute of the electrostatic systems.
These types of systems make sence for some industries, (you mentioned hydraulics-- where sludge and varnish are REAL issues) I have not found the need in my field.
I get suspicious when someone claims that they can selectively charge particles that are contaminents or wear when some of the contaminents can actually be additaves in other lubricants.
regards.....