It's working for me like it should by the provided strategy. First I printed Yin/Yang symbol in PLA white and PETG black.
It was a good test to see a PETG filament bleeding into the white PLA. Increasing the size of the purge tower in this case makes sense.
Second object was a Kobayashi Fidget Cube with white PLA base and black PETG hinges:
The limitations of using PETG got obvious. The second hinges curled ab and the bad adhesion to PLA have done the rest. I had to stop it in the middle. Anyway, the first hinges are working fine and very smooth
For the third test I've created a test object to use PLA, PETG and ABS in one print.
The idea is to have the base in PLA, the windows in PETG and the tubes in ABS. So far I've printed only base in PLA and windows/tubes in PETG. This is my first result:
As you can see one layer is missing due to hairy PETG. But it healed himself and printed without my intervention in 4 hours. I'm still fighting PETG in MMU. It was printed with 250C and I don't want to go lower as it will get brittle.
Anyway, this script helps me to print even with different types of PLA (190C vs 220C). My plan is to bring it into Slic3r at some point. This python script is just a proof of concept and much easier to modify. Any contribution is very welcome!