Hi,
I guess the main impact for EE is to ensure all specs using threads (servlet, batch, concurreny even if this one is pretty much useless in practise, ...) enable or not the usage of virtual threads (as the EJB was not allowing custom threads for ex) to explicitly it support it.
It can surely be done globally in a shared spec (ee concurrency can be a location but the platform umbrella can be a better one too).
In terms of vendor support it means supporting a configurable and injectable virtual thread factory preconfigured for the EE env and to not rely on the default virtual thread scheduler (virtual threads being just more or less runnable in a thread pool at the end as we have today, just lower level integrated).
It can mean making forbidden or undefined the usage of Thread.startVirtualThread(Runnable) (which uses the default thread pool so a global forkjoin pool which is incompatible with multplie classloader until the app server rewrites the code to make it friendly - tccl handling, context handling etc).
So overall I think it either means enabling the standalone (flat classpath and no EE classloader) case - but this means defining it in EE even if most app server have this mode, this does not exist in the spec and/or defining an app server mode to enable users to use it in a way which is EE stack friendly.