Select recursive :last-child. Possible?

No, unfortunately that's just about the only way to do it without modifying the HTML.

There has been at least one request for recursive versions of the :first-child and :last-child pseudo-classes, but it doesn't seem to have gained much favor. Notice it suggests nesting and repeating the pseudo-classes in the same way as in your question:

Currently, AFAIK, we can only match children up to some exact nesting level known in advance (3 in the example below):

.container > :first-child,
.container > :first-child > :first-child,
.container > :first-child > :first-child > :first-child {}

We cannot use just :first-child context selector since it would also select first children of blocks that are not first children themselves.

So we need a sort of recursive selector that matches not just first of last child, but recursively matches all first-most and last-most elements regardless of their nesting level.

body :last-child {
    color:red;
}
body :not(:last-child) :last-child {
    color:initial;
}

Any last-child element that's a descendant of one that's not a last-child will have the change reversed.