I was missing that too, no way to fill holes. Also the visibility menu is completely missing. With the trial I was just getting accustomed to using it to create poly-groups and use edge loop to create nice topologies 
My hope is that they will slowly but surely add little features in to make the core version usable for all sorts of scenarios. It seems the focus is 3d printing (fine by me), but for indie game developers there might not be enough functionality.
Quick question, is there a way to start the program maximized with the windows taskbar visible? I don’t like to work full-screen and manually resizing the windows to be maximized-ish is a hassle.
To have the taskbar visible all the time, you need to resize the ZBrushCore window. Just click the button to resize it, then drag the corners and position it how you want it. Press Ctrl+Shift+I when done to save the configuration, which will include the changed position. I personally never mess with that. It’s so easy just to press the Windows key on my keyboard when I want to see the taskbar and I prefer having the extra real estate for my ZBrushing. 