#1 - EnvIt vs MASH ?
At first it's important to know the history of Maya Scattering system. You should understand that most of scripts or plugins don't create their own algorithm, they should use Maya ones. It's the case for MASH, EnvIt and any.
As you may know there is no scattering tool in Maya, since age scripts are based on nParticles with Instancer node. That's works, but it's an extremely old technology from more than 10 years old, with limitations and no more development from Autodesk.
All the scattering tools existing are based on this algorithm, including MASH.
EnvIt is the first and only to use the all new Maya Scattering Core powered by Bifrost that Autodesk is building for the next 10 years!
This is the main reason why EnvIt instead of MASH, plus the dedicated UI, simple onClick workflow etc...
#2 - EnvIt vs direct Bifrost Graph ?
Knowing that some asked : why using EnvIt instead of building my own Bifrost Graph? Of course, it's possible. But what's the main purpose of a script? It's to automate for you tasks using existing tools. Which mean in fact you can do what scripts does but that'll take months instead of seconds. Scripts are mainly a gain of time and comfort, nothing more. And it's the idea of EnvIt and all my scripts : found the best workflow for you in order you focus on your Art and do it with pleasure. Back to EnvIt, it took me 5 months to develop my Scattering Bifrost Graph and I was helped a lot by talented people and Beta developers. Also even if you build your own Graph you'll still not have automation provided by scripting aspect.
#3 - EnvIt and Redshift / Vray / Renderman?
You are a lot to ask me if EnvIt is working with Redshift, Vray or Renderman? For now it's not. It only working with Arnold.
As we saw EnvIt used Bifrost and Bifrost is still in development and don't support others renderers for now. So we should wait to Autodesk support those renderer in order I add them to EnvIt.
#4 - EnvIt Roadmap?
For now ENVIT is only 30% of what I planned! I don't see it only as a scattering tool but as a complete Environment Toolkit.
It's why you will see in fact I also plan to made Cloud, Water etc... tab!
I don't planed to made any ground creation feature because there already powerful tool for that *(Houdini, Gaia, Terragen etc...)* that can easily be import in Maya. The purpose of EnvIt is to fix missing feature in Maya.
Here you can access the EnvIt Roadmap