Fluids system in Maya is very old.
We need a renewed system that can actually compete with software like Houdini.
Technically the Aero system is aimed to that, but it needs to be massively improved.
Add the possibility to use Density, Temperature and Fuel or something similar so that we can make smoke, explosions, fire, etc.
Make Bifrost and Aero work with fields: geometry acceleration is awesome, but there's no reason to not be able to use fields and so on.
So, I'm not going to post links to good systems to make a comparison (like fumeFX, Houdini, Krakatoa, phoenixFD, etc): either renew old fluids system to be faster and more stable and intuitive or improve Aero system so that is actually usable.