The filing requirement is the real kicker. Until small business software like Quickbooks and Turbotax for business makes it trivial to file in every state. The compliance cost will be VERY high. In Hawaii for example, you have to file and pay your excise tax return every month. Multiple that by every state and you have a lot of work.
I suspect those companies that sell inexpensive items will probably restrict the number of states they sell to until the software support is there.