Here is what Maven reports when invoked in multi-threaded mode (say, "mvn -T 9 clean install") when Moditect plugin is used:

[WARNING] The following plugins are not marked @threadsafe in Tascalate JavaFlow / Tools / Apache Maven:
[WARNING] org.moditect:moditect-maven-plugin:1.0.0.Beta2
[WARNING] Enable debug to see more precisely which goals are not marked @threadsafe.

If Moditect is thread-safe by nature than it makes sense to add aforementioned annotation...