Feldon At Fan Faire, it was announced that if you upgrade your guild hall from T1 to T2 or T2 to T3, your amenities get fully refunded and you can take all the items and move them to the bigger hall. BUT you did not get any of your purchase price back. An update this morning from Rothgar:
The T3 guild halls do not require faction to purchase. T1 and T2 guild halls only require someone with the appropriate faction to purchase them, just like a regular house. But once its purchased anyone can come and go regardless of faction.
Keep in mind that you do not lose the cost of your amenities when you upgrade guild halls. This allows you to start out in a smaller hall, start buying amenities and then upgrade later when you have the means. I will also try to make it so you don’t lose the entire purchase price of the hall either. I think we discussed giving back 75% of the purchase price of your old hall.