Here is some important SAP notes on this topics.
Note 1696869 – Strategy for Patching of Oracle Homes with Minimal Downtime
Note 1524205 – Installation Oracle home” and Run-time Oracle home .

Apparently it seems interesting, but how far? Need to understand and then findout someone who did it successfully. How much do it really possible to accomplish in a huge database with 24X7 availability.

Till to understand, how much really downtime is reduced and which are the point of no returns?