In the end of Chapter 1 of Igeret HaKodesh (often published with the Tanya), the Baal haTanya writes that businessmen should not be invited to lead prayer on weekdays, but only those with the free time to extend shacharit to at least 90 minutes. He suggests teachers and those supported by their parents have this ability. He goes further and says he will send spies to see if this is being followed and push off with both hands those who could do this, but do not.
Is such a thing still done at Lubavitch minyanim where it is possible, such as in a yeshiva? I have not seen it done in chabad shuls, presumably because those who need to go to work would not accept a 90 minute shacharit, whether they were leading or not.
If it is no longer done, was it a decision to do so, or has it merely fallen out of favor?