I would also like Streetview integrated directly into TW.
I am already using Streetview with TW though it opens Streetview as a new web page. This is done by setting a "Link URL" action to a hotspot on the Google map. First go to Streetview and point the image in the desired direction then click on the link option and copy the URL. Add a hotspot then set the action to Link URL and copy in the Streetview URL. An advantage of this is that Streetview will always open pointing in the same direction (great for property tours!!). I would prefer this was integrated into TW, but it may offer you a solution until the day comes.