Not sure if this was an intentional change, but using M3a, I had been specifying the the scala simulation to be run in the properties for gatling-maven-plugin
**/Simulation.scala
This no longer appears to be honored and is defaulting to **/*.scala and not giving me an option to override (at least not in the properties). I realize that the simulation class can be specified as the gatling.simulationClass property.
It also appears that the option to exclude files was also removed.
If this is an intended change in the implementation, you may want add this to the migration guide.