Mixed economy is still an ideal concept for the least developed countries. True or False?

Maily yes however there is some isolated cases from people who decided to give a proper try. You can read a book called360 ideas to change the world (written in2006, if I recall correctly, by two French student from HEC business school)

I do think it will come faster than in developed economies as creating a mixed economy is easier than correcting another type of economy (because people are already used to that).