Currently, italic fonts are achieved by making the current font oblique. It would be great if it would use the italic font instead.

Here's how I envision it could work: Similar to using a custom font with ~/.termux/font.ttf, put an italic font in a file called ~/.termux/font-italic.ttf. Then run this:

$ termux-reload-settings
$ echo -e '\e[3m light fixture \e[0m' # characters that look different in italics

and it would print this:
light fixture

Examples with Source Code Pro

Regular:

Italic: