Can OSM data meet the requirements of ISA?

The answers are no, and no. Because without suitable open datasets we have no way to verify the accuracy of our speed limits, and because our mappers are free to spend their mapping time on whatever they choose - they are not employees who receive guidance from a central authority. The most we could do is raise awareness among mappers - but a significant percentage of mappers is not even interested in automobile traffic at all.

I don't know what the ISA requirements are or if OSM is maybe already meeting them in some regions. There are examples where other providers already use our data in similar way. In Germany Allianz for example sells vehicle liability insurances at a special tariff where a so called Drivebox collects telemetry and also compares actual speed to the speed limits collected from OSM. So they deem the accuracy already sufficient to penalize drivers based on them.

From my experience the biggest gap is probably that limits are not mapped at all in OSM so leading ISA to not warn. Wrongly mapped limits are rather uncommon, thought they will exist, too.