Australian Institute for Teaching and School Leadership (AITSL) reports that online education is becoming more common for training new teachers, up from 13% in 2005 to 25% in 2016. The typical student is an older female with a full time job and family responsibilities. Not surprisingly, they are studying part time. This research is contained in the report "The rise of online initial teacher education: what do we know?", AITSL May 2018.
The same problems apply to online teacher education as to any online program. It is more difficult to engage students online, they take longer to complete and fail to complete at a higher rate. Also, as with any vocational program requiring work placements, this is more difficult with remote students.
The good news is that an online program provides access to eduction which would otherwise be denied those with family responsibilities and jobs. Also the quality of such graduates is no different to that of on-campus students.
AITSL's estimate of 25% of teaching students studying off campus may be an underestimate. I suggest it is likely that more than half of all Australian university students are effectively studying off-campus. While officially enrolled on-campus, students take advantage of the online components of courses, to minimize on-campus time. The typical student is balancing study with a job and other commitments.
ps: Last year I completed a MEd online at Athabasca University. My fellow students were as described by AITSL. I felt very much in the odd one out, as I did not have a husband, two children, a dog and an alpine sport. ;-)