What I assume - The Player's Guide would first and foremost be for players, most likely people new to Traveller and possibly new to RPGs in general. Not that We Seasoned Players wouldn't buy it, or fund it - we would - but we're probably not the key demographic that's going to keep the game alive and vibrant into the Far Future. Those younglings, they're most likely scifi fans, so we can probably assume some scifi literacy. Also, how many people start playing RPGs when they've got a full-time job, family and kids? Some, maybe. But not a lot. So again, probably young.
What I suppose - All the recently successful new editions of major RPGs have been visually complex, engaging, and appealing in an affective way, not in the "clean lines, black and white" motif popular way back when. A successful intro book/Player's Guide with everything backing it for success would probably be more like the stuff that sells well today, in regards to a cover and associated art.
What I know for certain - I love the idea of talking about this, but when this book moves closer to becoming something we can hold in our hands but before any serious decisions are made, I hopehopehope stakeholders in the process get input from several to many actual new-to-Traveller types, seasoned gamers in other systems all the way through total newbies.
I could go on and on about this, but why ramble? (^_^ If people new to Traveller or scifi gaming are an important group of buyers, a serious attempt to learn what would be appealing to them should be made.
My vote - the Starport. regardless of the type of adventuring a player might want to do, it's a common point of interest. And I -really- do love the spirit of that artwork Ackehece posted.