!!! Make cursors great again
I switched recently my Laptop to a
 ThinkPad P52 with a 4k display. The display resolution is 3840x2160 
pixels on a 15" display - this makes all graphical objects very tiny. I 
cannot use the NVidia driver at the moment (very likely a buffer being 
to small in the illumos kernel), I have to use the VESA driver.
Also I do use the  [NsCDE|https://github.com/NsCDE/NsCDE]  desktop, so I don't have fancy settings available for cursor sizes.

The cursor sizes were not a big deal, since NsCDE has a nice font selector, other things became a bit more difficult like firefox ({{{about:config, layout.css.devPixelsPerPx=1.4}}}).

For LibreOffice I needed to set {{{SAL_FORCEDPI=200}}} in the environment, for generic QT applications I had to set {{{QT_SCALE_FACTOR=2}}}.

For GTK applications, I changed ~/.gtkrc-2.0 and 
~/.config/gtk-3.0/settings.init to include especially 

{{{
[Settings]
gtk-cursor-theme-size = 20
gtk-double-click-time = 750
}}}
For the mouse cursors it was pretty complicated. NsCDE ships some custom 
cursors in /usr/local/share/NsCDE/icons/cursors which I have resized 
with ImageMagick.

The basic cursor instead got changed with some other ways.
In $HOME/.fonts/ I have created a file called fonts.alias, the file contains:
{{{cursor -xfree86-cursor-medium-r-normal--0-180-218-218-p-0-adobe-fontspecific}}}
Query with {{{xset q}}} and look at the Font Path. In my case $HOME/.fonts was not in it, so I would add it with {{{xset +fp ~/.fonts}}} .Initially you want to rehash your font cache:
{{{fc-cache -r && xset fp rehash
}}}
For testing you could now set your new cursor: 
{{{xsetroot -cursor_name left_ptr}}}

However you need to persist this in ~/.NsCDE/Xset.conf, append the following two lines to it:
{{{xset +fp ~/.fonts
xsetroot -cursor_name left_ptr
}}}
Log out and log in again and enjoy big cursors.