Hey Harold - a really good discussion here, thanks for that.
In terms of DVDSP and BD authoring, it's kind of like the difference between making a CD and making a DVD... superficially similar, but incredibly different sets of rules govern the two formats. DVDSP is capable of creating the environment within which a user will be able to view and control playback - that's the essence of authoring, however the BD specs introduce a massively different set of features that authors can leverage in order to make the experience very different to standard DVDs.
That isn't to say you can't use DVDSP to create something and set it to blue instead of red... just that doing so won't result in a true Blu-Ray disc. You can put High Def content on a standard DVD (not much, I grant you) but it won't play back in a load of players. That's the main issue here, I think. getting the content on the disc (whether through FCS, or any other tool) is only part of the problem. If you want to use HD footage, and BD in particular, you'll need a BD burner, BD discs, and a BD player.
Whilst DVDSP does provide templates, they aren't always the best way to go. There are so many variations that are possible and auto connections (like in iDVD) would reduce the overall functionality and the ability of the author to create customised experiences for their viewers. It isn't all about ease of use of the software - we need to also consider the end user when authoring.
That said, for some folk the templates are a Godsend. It speeds up the entire process, and if that's what is needed then great! However, the power of DVDSP is that it frees the author to be a little more creative when necessary, too.
Given the ToU for the boards, it isn't appropriate to speculate about whether DVDSP will or won't include full BD authoring, but Mr J himself has said that it won't happen any time soon... there are a lot of financial elements involved (licensing for example), quite apart from the various technical problems to change the software to allow access to the full BD spec.
Personally, I think BDSP would be an entirely new product, and DVDSP will stay as it is for now. But that's speculation (apologies) 😉