The problem, in my opinion, is that calendar as implemented by vBulletin is essentially a sand-boxed feature that exists entirely in its own ecosystem.
Yes, this was a key failure to the vB calendar. Of the Blog Posts as well.
Listing Events such that they show up in the What's New ? is a no brainer idea.
To start, I would like to get rid of the idea of a "thread" versus an image "album" versus a calendar "event" versus a collection of "links" versus an "article" versus just about any other content type. Instead I would like to have a single "entry" object.
I love this line of thinking. I feel much the same way ... but with a bit more structure than you propose.
Content Types:
1) Post
2) Gallery image
3) Event
4) Link
5) Article
X) Content Type X.
6) Pages
7) Wiki item
8) Downloads (files, etc.)
Did you know that xenforo essentially has your "Content Types" idea already ?
Forinstance, Jaxel created a xenforo content type for his wiki entries.
I do not know if XFR albums created images as a xenforo content type.
Jaxel says that Xenforo's What's New listing only lists posts ..... but that if the what's new allowed listing of all the content types .... XenCarta users would be able to see wiki items show up in What's new !!
So, essentially xenforo has the bare bones structure for what you desire for content types.
I love your idea about content agnostic posting. It is a great idea ... but the devil is always in the details.
In some respects, your free form posting idea would create alot of moderator work to put some structure on the content.
The lack of structure may also give you less SEO.
Some practical things like ... do you really want EVERYONE to be able to add to the Calendar ?
I also think a well done "Pages" function could accomplish much of what you desire.
You idea is certainly worth thinking about more ... and doesn't deserve to be buried in this thread !
How about making a thread of it's own ?