I collected a lot of seeds from my 'Tamukeyama' this year and I was wondering will most of them grow into a weeping/cascading form or will some/half/most of them revert to regular upright?
No guarantees but it seems that a majority of JM seedlings will resemble the parent plant. Not identically of course but quite closely. You are also likely to get some that have no resemblance at all, either in habit, leaf size or shape and leaf color.
The weeping disectums usually have very low germination rates.