Here's why I think it's going to work just fine: it's been working in Pinnacle Liquid since 2005, Premiere Pro since 2006, not sure when Vegas added it, but it's there, etc.
The feature is much older in Avid, although the name Open Timeline to describe it goes back to 2005. So, Apple's version of the feature is actually called "Open format Timeline."
I'm just saying.
Here are some caveats:
Aspect ratio conversion isn't automatic for anyone. Some apps make it far easier than others to deal with -- tools for pan and scan, etc. -- but you'll need to steer your way through this one as needed.
In a mixed format timeline, there's a single "native" state, and the "mixed" footage will have to be upscaled/downscaled as needed, and all of these will have impacts on performance. (It still works, but the specifics will dictate where performance stands on the Unlimited RT Disappointment scale.)
Note too that there are limits to everyone's implementation of the feature, which may or may not have impact on the way you work. Do any mix NTSC and PAL in the same timeline? I don't remember, and am too lazy to look it up. Some folks won't let progressive and interlaced footage mix. There are multiple approaches to audio sample rates -- some let you mix and some don't.
The degree of difficulty goes way up when you throw multicam into the mix, of course. But I was showing RT mixed format multicam on a G4 laptop in 2005, so I know it can work.
Which is why I'm certain that Apple's Open format Timeline will work. But it won't work miracles. Only expect it to do what it will says it will do.
In any case, it's a very, very cool feature, and does indeed look magical. You'll get used to it fast. :-)
