ZDoom

Main Idea:

On titplepic map:
titlepic shows some intro stuff, if user press any key to show the menu, it'll not show the menu, but it'll call an acs script to skip the intro and show main menu scene, if now users press any key, it'll show the menu.
ingame:
if menu is requested, show the menu and some animation on the background (I belive I cannot execute an acs script at this point so maybe some zscript.

Basically a copy and paste of how Spooky House menu should work.

No. The main issue is that the outer main loop of the engine is not scriptable and this is what takes care of context transitions, e.g. from titlescreen to menu or console.

My knowledge of ZScript menus is limited (aside from the broad advice of "SendNetworkEvent seems to be useful"), but a likely workable alternative is to make a TITLEMAP and craft the intro/menu-background scenes that way.

I'll have to defer the "how to get the menu to interact with the TITLEMAP" bit to someone who actually knows how to do that part, though.

It's possible but complicated. Everything has to be routed through network events.
But like I said, the bigger problem is that the menu is driven by the outer main loop of the engine which is native code and not particularly configurable.

oh, I was thinking that the menu stuff was modular enought for doing tasks like that with the inclusion of zscript.
Also, I wouldn't mind if the menu wasn't multiplayer friendly, I could Always on the future make a special version of the mod for being compatible with multiplayer