This link list most of the open questions: http://www.rbmojournal.com/article/S1472-6483(17)30078-0/fulltext http://www.rbmojournal.com/article/S1472-6483(17)30

This link list most of the open questions: http://www.rbmojournal.com/article/S1472-6483(17)30078-0/fulltext http://www.rbmojournal.com/article/S1472-6483(17)30078-0/ful..., looks like mainly some clinical work and also ethical grounds due to legality etc.