For whatever reason in our jurisdiction the great schema seems to be standard for hieromonks. It probably varies from place to place. But jah is right that the great schema is not a canonical prerequisite for the abbacy or anything like that.
Well, the usual practice in the Greek tradition is that when monastic vows are taken, then they should be tonsured to the Great Schema. They are of the mind that once one is tonsured, then they should go all out and take the Great Schema. In contrast, most Russian monks who are tonsured will take the small schema (stavrophore) and that is as far as they go because the Great Schema will be reserved for those who will live as hermits. I got all this information from Fr. Seraphim of Holy Cross Monastery in WV this past summer when we were discussing monastic ranks.
OK, but then they aren't tonsured to the great schema right away. I know someone who's been a monk for a while and I'm pretty sure he doesn't wear the great schema, and he's never been ordained a priest.
I believe you're both right on this. It seems that the Great Schema is more common among the Greeks (I believe Greeks tonsure novies into the rassophore and stavrophone ranks very quickly, and the Great Schema is awarded within 15-20 years of monastic service. in the Russian tradition, it is VERY different. I have never met a Russian tradition monk of the Great Schema, and probably never will (unless I go on pilgrimage to Russia and seek one out!). The only Great Schema monk I know of in America from the Russian tradition, as was mentioned above, is Bishop George at Holy Cross Monastery in West Virginia. However, Vladyka was tonsured into the Schema on Mt. Athos, into the Greek Schema, during his time there. I only live a few hours away from the monastery and I'm there regularly. I've never seen Vladyka actually wear the Schema, either of the Greek or the Russian tradition.
I believe the tradition laid out above (as attributed to Fr. Seraphim) is correct. I've never spoken with him about it, but, from what I've read, observed and heard, it fits.