One, they're not "anybody". They're (supposed to be) developers. They did this with an earlier version as well. I think they told people on 10.1 to test a fix on the as yet unreleased 10.2 (my memory on this is a little hazy, so maybe someone else will have a clearer recollection). I think a 10.4 with iPad features makes some sense.
Giving to a "developer" an information like that is like giving it to everyone since it will get public in a matter of minutes, like in this case.
Anyway, i'd love a 10.4 update, hopefully with new iPad features not exclusive to the 2017 model.