TL;DR
Loading sprites seems to already be multi-threaded... Can the threads be kept in the background, to stop having the Main Menu inaccessible before that task finishes?What ?
Going through the whole graphics defaults issue made me (yet again) long for such a feature... Basically: is there any reason why the game needs to fully load the damn sprites before allowing me access to the main menu?! When i just want to toggle some mods ( which results in repeated sprite-loading
Maybe if you did it like openTTD to have a demo game running as the background for the main menu, then i'd understand it, but TTBOMK you don't (yet) have that. 

Using images
See attachments,From: current.jpg
To: mainMenu - tweaked (poorly).jpg
Why ?
Less time wasted by unneeded delays. And less frustrating for players in certain situations.Speaking from my current perspective as an experimental-branch user, i could use that time to read the changelog.
