I’m not 100% clear what you mean by “global focus”. OmniFocus 2 for iPad doesn’t currently have a “Focus” feature the way the Mac version does, but, as you mentioned, you can still use perspectives to focus in on a specific part of the library.
I have my areas of life split into “Personal”, “Work” and “Maintenance” (which contains system-wide things like my Weekly Review projects and recurring actions to remind me to process my OmniFocus inbox daily) and have two perspectives for each. For example, the “Personal” perspective reveals all available items in this area of my life and “Personal+” contains all available items that are either due/flagged.
Yes, I meant the focus feature as on Mac version, but as it’s called just that in the perspective settings as well I had to use some term to distinguish them …
I have a system like yours, but with several perspectives (many adapted from Sven Fechners OmniFocus Perspectives Galore blog post series) that aren’t unique to each area. The Focus feature makes that a great way to work – I select which area I’m currently working in and then use the perspectives to plan and organize my work. Without the Focus feature I have to use one of the cumbersome work-arounds described above. Even if I may reduce the number of perspective used it seems like a waste to have to duplicate them for each area.
Edit: It’s called OmniFocus Perspectives Galore, not Context …
I also use some perspectives that don’t focus in on a specific areas (e.g. “Available”, “Important” and “Errands”, “Waiting”).
It would be great to have a Focus command on the iPad, and not just have this functionality available through perspectives (Pro). Other than reorganizing your folder structure, the only thing I can think off is to create a perspective called “Focus” that is used for ad hoc focusing. You could edit this perspective each time you want to shift the focus, and leave your other perspectives untouched. Not ideal, I know, but hopefully this will help.
And if you haven’t already, I recommend contacting the Omni Group with this feature requests.