Apple has already revealed that Steve Jobs will talk about iCloud, iOS 5 and OS X Lion during his WWDC keynote on Monday morning.

In addition, it’s rumored that Apple’s wireless Time Capsule backup/router will get a big update.

Here’s how iCloud and the new Time Capsule will work, according to a source close to the company who asked not be identified. It’s pretty surprising:

According to the source, Apple has developed a system to make users’ Time Machine backups available through its new iCloud service.

This is the “Home Folder” access concept that we’ve detailed before (how it will be accessed using NFC iPhones and the role of the Mac App Store). All your files and data — pictures, videos, Word and Excel documents, and so on — will be available anytime, anywhere, on both Mac OS X and iOS devices.

The surprising thing is, iCloud won’t be fed through Apple’s massive new data center in North Carolina, as you might expect.

Instead, the system will be based on Time Capsule, Apple’s wireless router and hard drive backup that’s currently sold in 1TB and 2TB versions. As rumored, Time Capsule will be updated, becoming less of a local backup and more of a personal cloud server, like the newer souped-up NAS (Network Attached Storage) drives from companies like Iomega (we reviewed one here). The new Time Capsule is rumored to run on iOS and come with embedded A4 or A5 CPUs.

Our source didn’t have any information about the hardware, but detailed how the Home Folder access system works. Files saved on your computer are backed up instantly to Time Capsule, which makes them available to remote Macs and iOS devices.

If you make any changes on any computer, those changes are updated through iCloud and stored on your Time Capsule. The Time Capsule archives and serves up your files even when your computers are off. When you get home and fire up your desktop computer or laptop, the files are automatically synced across your devices.

This service will also allow you to upload photos and videos from your iPhone or iPad to your Time Capsule. The media will be stored on the device and be made available for other devices to sync. iCloud is the “conduit” through which everything moves, the source said.

“Your computer gets backed up to Time Capsule anyways,” said the source. “Now it’ll serve up your content when you want it, where you want it, right there on your iOS device.”

The system sounds like Dropbox, the web-based file-hosting system that’s won accolades for simplicity and ease of use. But in Apple’s case, your personal cloud will be maintained not on company servers, but on your own Time Capsule.

Why isn’t Apple using its massive new data center? This part is not clear. It may just be a way to sell more hardware. Apple is a hardware company after all.

Or perhaps Apple feels that consumers will happier if they are in control of their own data. Maybe users don’t trust Apple (or any other company) to host their most important files, especially after years of spotty service from MobileMe. Or there could be other reasons, perhaps legal, that are skirted when users are responsible for their own data.

Our source says the system is fully baked and is “what’s next in line” — but stopped short of saying this is what Jobs will reveal at the Worldwide Developer’s Conference on Monday.

The source said it will be added to future versions of OS X and iOS — but they didn’t know which versions of OS X and iOS. There appears to be no sign of it in beta releases of Lion, which has been available to developers for months. Apple has kept iOS 5 under tight wraps, and it may be ready for this system.

UPDATE: Actually, it looks like the technology is already built into Lion. The Auto Save, Versions and Resume features in Lion look an awful lot like a smart file-management system designed for the cloud, resembling the way iOS and Google Docs save and manage multiple versions of documents. In addition, Time Machine in Lion is tightly integrated with Versions, making it more of a realtime backup system. “… [Versions] also appears to be used to make Time Machine much faster to open, as the Time Machine user interface can now access local snapshots take between remote backups, a sort of ‘instant Time Machine.'” See AppleInsider: Inside Mac OS X 10.7 Lion: Auto Save, File Versions and Time Machine

“This is what I heard that they have ready to go,” the source said. “This is what’s next in line. Word is, it’s a pretty finished piece.”

Given the source’s confidence in the completeness of the system, we’re willing to go out on a limb and bet this is what Jobs will reveal on Monday.

Airport Express — More Processing Power

In addition, our source said Apple’s Airport Express portable WiFi router is also getting an update. Specifically, it’s getting more processing power. The source didn’t know why. AirPort Express is also rumored to be getting an update next week, largely because Apple’s stores have run out of supplies.

The source didn’t shed any light on other rumors surrounding iCloud, such as it will include an online music locker or cost $25 a year.

However, they did pour cold water on the rumor that Time Capsules will download and store iOS updates in the background.

“I haven’t heard anything about a Time Capsule holding iOS updates,” they said. “Honestly, that rumor sounds incredibly stupid. Why would a Time Capsule need to store an update to deliver to your phone when it can be downloaded live?”

Also, don’t miss: The Cult of Mac Super Guide To What To Expect At WWDC 2011