It has been a while, and I have seen this as a request here and there.
Please, consider adding this to the Mac version, for the sake of my sanity as well as for feature parity of the two platforms. With very seldom exceptions, I can't stand floating palettes and was really happy that, in Windows at least, I could snap and stack them horizontally, i.e. in columns that are part of the main window. Now that I am back on a Mac I'd love to finally see this resolved.
In the Mac version, there is the one main column, and if I want two columns of palettes I end up with a couple of floating ones, which I can't stand.