Subdivide Tools->Board menu into Cores.

If there is more than one core, such as having the arduino core and the tiny core, each has a seperate boards.txt file. It would be nice if the Tools->Board menu was split into which core a device comes from. At the moment, because of having two cores, the menu is longer than my screen is tall!

You could have seperate menu's like:
Tools->Board->Arduino
Tools->Board->Tiny
etc.

The name of the menu would be the same as the name of the core (with a capital at the start of course). So the arduino core is in a folder called "arduino" so the menu entry would be "Arduino", the tiny core is in a folder called "tiny", so the menu entry would be "Tiny".

If there was only one, it would remain as it is currently (with no subdivision)

Just a thought.

Another option is to your boards.txt to remove items you don't need or use.

On my to-do list is scrolling menus. There's a free java example published which adds it to jmenu. On my machine, my sketchbook folder is taller than my monitor... and I have 1600 pixels vertical.

Yeah, they need to find at least how to add scroll to the menu