Hello Jeetanshu and thanks for your question.
As more high speed devices are being designed, this question is becoming more and more important. While ANSI/ESD S20.20 does have limits there will be new revision that may help in the control of insulators.
The most important factor would be the inductive charging of the device itself. No matter what the insulators are around the ESDS item, using techniques that measure the device itself will allow for direct measurements. A contact high impedance voltmeter may be a very useful tool for the future of these measurements.
Another measurement that will be included in the next version of 20.20 will be to make a field measurement at the location of the ESDS item regardless of the insulators around them. Here you could set a limit of 50 volts per inch or 2000 volts per meter. The limit would be part of a compliant 20.20 program.
There is also a useful standard practice that is in industry review right now, ESD [DSP17.1-2020] - ESD Association Draft Standard Practice for the Protection of Electrostatic Discharge Susceptible Items – Process Assessment Techniques. This new standard practice the will give tools to help evaluate ESD control programs that have devices with reduced device sensitivities. From doing these measurement, realistic limits can be set for a 20.20 compliant program.
Certification can still be obtained using the 20.20 requirements with the modifications that are made from your measurements.
I hope this helps.