iOS 6
The banners Mac Rumours found online pretty much prove this.
OS X Mountain Lion
Probably will be talked about with it's release this year. So I say Mac Rumours got this one right.
iCloud
Very plausable to hear some iCloud talk with regards to OS X Mountain Lion and iOS 6. So MacRumours probably have this right too.
MacBook Airs, MacBook Pros, Mac Pros, iMacs and Retina
Good rumours? Yes. WWDC rumours though? Probably not. This is a WWDevelopersC not a WWHardwareC. It could be a footnote on the Keynote but that's about it. So MacRumours saying it will definantly be talked on the WWDC keynote is obviously wrong.
Apple TV
They will probably talk about opening up the TV to developers. That is a safe bet. But a physical Apple brand television? MacRumours has been smoking the "we want a Apple brand television" pipe for way too long. Any smart person will realise this will not happen on the WWDC keynote. The MacRumours (as do many other people) need to wake up and realise this. If this was to happen it'd get it's own keynote later in the year.
iPhone
I'd say Plausable. Based on past years. Not a certain but I would not rule it out either.
Live Keynote Coverage
By Apple won't happen. We'll get the keynote on the website a little after the keynote is done. But will many websites have a live weblog of the keynote? Yes. MacRumours is no exception to this.
It's not "plausable", it's "plausible"...