Remember that Portsmouth was only added so that there was some scenery when you sail down the Solent and for the Hovercraft- it was never advertised with Portsmouth as a feature- so it's just a bonus.
That said, Portsmouth (as I've said before) as Portsmouth has already partly been modelled, it wouldn't be so hard to complete it and sell it as the main feature of a future add on. However, I wouldn't bank on it as I think Vstep is likely to make addons for different parts of the world to appeal to as many possible users worldwide.
If night features are improved in future releases, what a spectacular sight the Spinny tower would be. For anyone that has never seen it at night- it really is a truly great icon in a truly great city.
Stu