Hmm let\'s try and keep a few things in mind:
1) The whole \"Hollow World\" thing is not even official, and was just a tiny comment passed by Talad. This was enough to spark the interest of the large chunk of the PS comunity that are interested in physics. However, this was only a comment, and has been given overdue attention. The most probable chance is that the world will not be this way.
2) Even the Xacha Scientists have not even dreamt of planets. The furthest their philosophical thought got was a cavern under Yliakum, already a large concept. Excitement is in mystery, and while getting to the bottom of things is fun, we have to remember that this is an MMORPG. We will never have any use at all for this knowledge, as the inhabitants of Yliakum can barely think to the scope of the great cavern beneath them. We, as roleplayers of these people, will never need to know if the world is hollow or not.
3) In discussing this, we\'ve shrunken Yliakum to a fraction of its size. We don\'t really think of it as being very big, just a tiny stalagtite comparitively. Yliakum is actually a huge world, at the very least the size of Faerun. There are still many, many things to explore in Yliakum, and only when we have exhausted them should we go on to seek grander things. We would be better off discussing the different levels of Yliakum, or Yliakum\'s ecosystem.
Edit: Spelling