In DD8's school there are 4 kids out of 35 in her grade who were redshirted. 3 of them are in her class of 17. There may be more but I only know of these because their parents have said as much. We were considering putting DD5 who is in K through a k12 virtual school in the same school next year.
I must admit that redshirting is one of the items that is giving us pause when considering what to do for DD5 next year. Through her VA DD5 will possibly have completed first grade reading and math by the end of her K year. She has a summer birthday and will still be 5 at the end of her K year. In the school her sister attends there are a number of students in both DD5's age appropriate class, rising 1st, as well as in the rising 2nd who were redshirted. In DD5's case if she were grade skipped she'd be 6 all year in 2nd grade and in a class with some children 2 years older then her. She is tall for her age if it even matters and we believe she is socially advanced. She is not prepared though for some of the social issues that comes with age for some children and has no tolerance for unpredictable or manipulative behavior. Basically, she's not worldly enough to deal with some of the social issue which could arise. For this and a number of other more pertinent reasons were are most likely going to continue doing the VA and consider entrance into a B&M school when she is older and more socially savvy in conjunction with a grade skip.
As far as hothousing goes we still see it in DD8's 3rd grade class. They have a pullout math enrichment program with students being pulled out for it for each unit. They are tested prior to each unit and if the ace the test they go to enrichment. I have had two mom's say that they research the curriculum online and then either hire a tutor or teach the child themselves at home the material so they can get into the program. In the meantime DD8 does not care to do well on the unit tests because she says enrichment isn't any more challenging for her then her regular class. She's sat in enrichment teaching other students how to do things according to her. She has little desire to do any of her beloved math at home anymore because she does not want to get further ahead and _we_ are told by the school not to teach her advanced concepts.
I wonder how Gladwell's book, "Outliers" will impact the trend of redshirting for non social or academic reasons.