Meanwhile, I have at last managed to clobber together a functional setup for the message box. Catch a zip file
There are two versions of the configs I made: one locates the box above the reticle, and the other under it. There are also separate versions of each for FSPort, because if you place the config not specifically made for Freespace Port in its data folder, the HUD will break quite a bit.
How to install: grab the preferred version of the config without _fsport in its name, and just dump its "data" contents into your MVPS "data" folder. Then do the same for _fsport version, but toss it into mediavps-fsport instead.
Later on, this addition might come into conflict with mods that heavily reorganise the HUD, but if that happens, you can either remove the entire script and its config, remove just the mv_root-hdg.tbm file and end up with the head animation weirdly out of place, or alternatively, preparing a separate HUD config for such a mod should be a breeze for me now.