How could or should the 6.5 mm Grendel be improved?

[Variable]

but the lead content probably rules it out for the US and NATO.

Which tells me that they aren't actually too serious about real world performance in small arms. They are simply busy chasing their tails while jerking everybody around and wasting tax dollars, all while playing enviro-whacko and social engineering games. These politcally correct games coupled with all of our civillian side blunders (many intentional) will likely lead to a desperate need for actual performance sometime in the not too far future....

If the DOD (or other entity) issued real world performance requirements--- then a platform and cartridge could be aimed at filling those needs. Without those, it's just spitting in the wind.