Greasy Fork

I don't see why it wouldn't be allowed. Perhaps it'd cause issues with other sites using an iframe on GF, if that's the case only allow target="_blank".

Why would you want to use it? It's common for scripts to link to external websites, and sometimes they need external sites to use the script itself. By opening a new tab, you create a greater user experience. As a website owner, when visitors open a link in a new tab, it keeps the visitor on the site for longer and also helps improve certain metrics; bounce rate, conversion, and pages visited. In addition, since the tab includes the GF logo, it also keeps the name and the brand in their minds.

Example scenario of when this would be useful:

Say, for example, you have a script that uses an external website to configure the script (a common occurrence). In the description, you'd probably want a link to that website so users, after installing the script, can configure settings.

Without _blank: A user may go to the script page, and open the link. It opens in the same tab and takes 10 seconds to load. Realize they need to install the script to make use of the website they just opened, then they'd have to go back to the script page and thus wait an additional 10 seconds, install the script, go back to the script page again, and thus wait another 10 seconds, and re-open the link in a new tab by middle-clicking or right click, then context menu, and 'Open in a new tab (not many people are aware of middle-clicking).

With _blank: A user may go to the script page, and open the link. It opens in the same tab and takes 10 seconds to load. Realize they need to install the script to make use of the website they just opened, then they'd have to go back to the script page, instantly by switching tabs... install the script, and immediately go back to the tab for the settings website.

Initially, I thought this be an optional attribute you could add, however now that I've thought about it. It would make sense if all tags in descriptions, comments, etc were automatically given target="_blank".

I personally find it annoying. If I want a new window/tab, I know how to do it myself.

It can be annoying for some, but to others - especially those with bad WiFi, constantly loading webpages is a hassle as opposed to just going back a tab.
Well, figured I'd suggest it anyways. 👍

Have you considered adding spoilers for both images and text? I definitely think it's not something necessary but someone may want it.
I'd put it at the bottom of the to-do list.