It's possible and relatively easy to add a custom LOADING lump that'll be displayed at startup when loading HPack. It's just like the ENDOOM screen, except it's shown during initialization.
There are, however, limitations because some content is unavoidable, so it constrains a bit what we can do with it (contrarily to ENDOOM screens). And of course, the canvas remains 80x25 ANSI characters in 16 colors maximum.
To illustrate these constraints, here's the outcome of a LOADING screen that is totally black originally, though with white as the foreground color:
The 3 can be hidden if at this spot the background and foreground colors are the same. The rest is hardcoded to be white on cyan and green respectively, and cannot be changed or hidden in any way.
If you want a crappy example of what it could look like, there's a LOADING.lmp in /incoming. Slap it in the pk3, or load it alongside it, and watch. If anybody wants to try creating something better, I recommend PabloDraw
as it is the simplest ANSI editor for Windows. Just download, extract the exe (ignore the .msi, it's useless) and play.
So, what do you think? Cool or tacky? I'll admit that ANSI screens give a early 90s feel to a mod, which is not exactly the goal of HPack.