Interesting... It looks like this part of ShoppingCartItem was updated to use the new displayPrice and such, but didn't go the last step to setting the flag to get the VAT added into the display price (and left out of the base price so that in the final order it will be split appropriately).
The big trick with this, related to what you're saying about the shipping address and such, is that the actualy tax adjustment is added in once we know the address and not before, just in case it will go outside of the VAT jurisdiction or other taxes might be involved or whatever.
It should be possible though to make a change to the shopping cart page to show the total with tax included, ie have it be based on the display price and not on the base price. Of course, then we need to make sure that when the tax adjustment is put in place that it is not added in twice.
Okay, this ShoppingCartItem change is now in SVN, rev 432121.