I had no idea what the tab [Site] meant and if one needs to think/wonder about what a certain UI element means, then it needs improvement. Apparently 'Site' means 'Categories', so why not call it that then if it means that? Here is the reason:
As with anything, you can edit the phrases if you can think of a better one, but it's shortened to "Site" as "Categories" would be too long. It may change in the future if the layout of those tabs were changed.
Great that the developers are open to look into this for the future. Your idea with the filter dropdown is a great one . Because it indeed has a filter function to begin with, those tabs [Any] [Site] [Album] as it is now.
Is see much benefits of your implementation:
One of them being is that there are 9 (!) tabs on that screen at the moment:
[Most Recent] [Most Commented] [Highest Rated] [Most Rated] [Most Liked] [Most Viewed] and [ [Any] [Site] [Album]
That is much. Too much maybe. Your idea reduces those 9 tabs to only 6. Making the interface less convoluted.
Not only that, your idea makes it clear that there is a difference in functionality between tabs that sort content (the first 6) and tabs that filter content (the last 3). Different functionality is now at the moment presented in the same way: they all look like/are [tabs]. Not so good UI/UX in my opinion.
The problem that 'Categories' is apparently a too long phrase (why is that actually? Because there are too much tabs in the way?), is solved immediately this way.
(For me it's confusing they now use the term 'Site' in one of these [tabs], since the term 'Site' is not used anywhere else on that screen. At the left of the screen XFMG uses the terms Albums and Categories and so for good UI/UX it's better to stick with those terms and not introduce a new term on an UI element for something that means exactly the same. [Categories] is therefor immediately clear. [Site] isn't.
Your implementation puts this phrase back in an elegant way. Top! .
Oh yes, and I very much like how it's possible to also include additional filters that way like Media Type as you demontstrated. At it's current state it is impossible in XFMG to filter on photo/video content indeed.
In the end it is just a matter of utilizing the already existing XF-features, XF-functionality, XF-icons, etc. from the "XF Forums" and from the "XF Resource-Manager" and drop in some more intuitive design similar as at photo-centric websites like Pinterest, WeHeartit.com and the "Media Gallery" will be a huge success.
Well... that explains it then why this 'mockup' is so clear and why I thought this idea was so great... it already existed (more or less)! I never used the Resource Manager so I had no idea... but still 'your' idea is perfect.