Again, my opinions, but:
I think a lot of folks have issues with the "by default" part of the question/discussion.
Let's look at Ubuntu for a moment: they have downloads for servers and downloads for "desktops". What is the biggest difference? The desktop downloads install a graphical environment by default. You can run a server on a desktop version (maybe a bit more work) and you can certainly install a DE on the server version.
Coming back to FreeBSD, a very long time ago the installer would ask about optional packages you want installed; one being "Graphical environment (X Window)". I don't believe that functionality is in the current versions of the installer, simply it gained some functionality and lost some. The sheer size of some packages nowdays means install media (ISO, USB images) need to actually be looked and decisions made on "what do we include by default to satisfy 99% of the people" and including a default graphical environment may mean dropping something else.
That's what I mean about issues with the "by default" part.
Now, if one searches here you come across some very nice tutorials (
Trihexagonal vermaden ) on installing a desktop environment that a lot of people have used easily. There is also the desktop-installer package (probably others) that when run asks you a few things and pulls down the needed bits from the package repos. A well written set of documentation (the handbook or release notes) makes the tutorials and packages easy and understandable to use.
Easy enough for Grandma? Probably not, but that's what they make grandkids for
I've never looked, but the installer may be scriptable. If so, then all you need to do is create an installer script (think in terms of kickstart scripts for some Linux distros) that does the base install, asks some questions, fires up the network, downloads packages and sets up a few things. Instant "install to a graphical environment of the users choice". To me, that would be the proper way to create a FreeBSD distribution that will install a graphical user environment by default.
Thanks for reading, time for more coffee.