I could imagine that I start viewing live TV at 10PM, I look back in the guide to 9PM and see a show I had previously scheduled to record, then it would be nice I could also just select that Show (in the 9PM slot) and click on it and start playing the recording (instead of leaving Guide and going to Shows).
That sounds like a nice feature as well. Maybe the left Skip button ( |<< ) on a remote could take a user into the past, to do such a thing. So the left button acts as it does now, and the |<< button takes you into the past, at which time you can then move around using the left and right arrows, unless you again move far enough to the right to be in the current time period, at which time current behaviour works again; You can't move into the past, unless you press |<< again. That would maintain current functionality for those who don't want to go into the past every time they move to the left edge of the Guide.
When in the past, the feature you suggest works.
PS: Nice job with the current time indicator Yaobing. It looks like it updates about every 15 seconds, so nice and responsive. Thank you.