1there is some problems with newtomain gravity - it dosenot works - i mean elements doesnot have any gravity only some of them have gravity and also i think if element becomes more hot it has more gravity
2 also i think we need - star plasma - plasma from star that can exist without anything and have a high gravity and create many heat and pressure but has a some limit because it will need fuel - many hydrogen and a helium - some other element that not inside game and under pressure and heat it will turn into star plasma
3 core plasma that will create veryyyyy many heat and pressure and very powerfull gravity and if pressure and nuclear fusion will be less powerfull than gravity it will go super nova and boom boom everything
That would break every save if implemented in normal Newtonian.
For a "better newtonian" mode like you said, every particle would have to be attracted to every other particle, which would be incredibly laggy with more than a few thousand (speaking from experience, I did once create an element called RBHL which would attract all other RBHL particles, in other words liquid BHOL, but I deleted it because it was too laggy)