This is an ongoing project.
The idea here is to explore the 3D printed PLA stiffness/geometry limits to keep stable smooth operation.
It is not achieved yet. :-)

I based on the pickle evo MK2 true x frame thanks to Ledroneclub design and I reinforce the arms to increase flexural stiffness crossing in the middle of the X. The rest is printed in nominal thickness. For the arms I increase the section but keeping the middle empty to save weight. I get around 12gr total 3D printed frame.

Testing motors on betaflight: if I keep the drone on ground they work smooth....if I keep pushing it to keep on ground while I increase power I get smooth operation. As long as I allow to lift off... starts to get low oscillations that are being amplified but limited if I keep the power at medium. The reason can be seen clearly on the betaflight monitoring of the engines...the FC starts to try to keep level flight and then this is traduced on a limit cycle oscillation on each arm...small enough to keep stable flight but not practical and motors & FC gets hot as they are close to be overloaded.
I fly with 2S and is feasible with the above caveat. I'm towards to increase the torsional stiffness of the conection between the upper and lower parts.
I did not try Nylon / CF yet and I guess should be much better behaviour. I understand that having more than 50 times less stiffness than CF is normal....just enjoy exploring and learning what can be done with PLA.

Update will come in the future!