Yes to OSX - those ideas were all cross platform.
A lot depends on your starting point. They're all the sort of things that a developer can do, but if that's not you and you have time constraints then you may be best advised to steer clear. In each case you're dealing with 3 or 4 technologies (SQL, XMS, XSL) each of which has its own learning curve.
One idea might be to trail the idea past Matthew at http://theturninggate.com/ - he's done some great work on the LR web galleries and might be able to hook Spry and LR up relatively easily. See if you can get him interested.
Another point is that it's a mistake to treat web output to one relatively new (lab experiment) web gallery as a key to buying an application. You should make DAM decisions on wider criteria. If it's any help, iView/Expression Media can export XML which can be transformed with a stylesheet - not tried styling it into Spry format, but that should be achievable.
Thanks a lot for the detailed answers.
It is funny that you should mention Matthew. My intend is to use his slimbox template as a base, and I contacted him this weekend on a closely related topic through some of his blog postings. :-)
The slimbox LR gallery does actually already offer the possibility to display some LR metadata into the slide show (I haven't really tried yet), but I fear that there might not be enough control in terms of layout for my applications. It seems that all the formating would have to be included as <...> formated HTML tags within the title"" tag of the slimbox menu thumbnails... and would have to be copy/pasted by hand after each gallery instanciation... If I understood correctly, Matthew is indeed saying that he didn't find a way to automate such things.
Anyway, I'll contact him again to double check.
As far as the selection of Lightroom as a DAM goes, I have already purchased a license, but the cost of the license is really a minor consideration considering the possible time loss/gain with an application offering time saving capabilities for repetitive tasks.
This being said, I agree that this is of course not the only aspect to consider.