The trick when training s l o w l y or even more s l o w l y is to continue to be appropriate in your intent, movement, fitting, connection, timing, etc. It is wonderful solitary training to test your intent filled movement as well as training with partner/s while understanding exactly what's happening and why, etc. As everyone has stated, this sort of training is very difficult to learn and do while keeping real action/reaction in both uke and tori.
I've found over the years that when we can do this slow training appropriately it's possible to seemingly change the appearance of the relationship of time in this relationship between uke and tori. As the saying goes... slow is smooth and smooth is fast. It's all relative and that's where real timing and strategy carries the day.
Great posts in this thread.. and I think old "slow hand" himself (Eric Clapton) would agree.