What if instead of targeting every possible platform, we built a version of OmniFocus for the web which could sync with the Mac and iPhone versions?
Let me ask, would it be designed as a stand-alone implementation of OmniFocus that would sync its data with the local software if the user wanted to? I'm thinking of the GMail model -- it has a fully functional web interface that can be used full-tim without any desktop software at all, but it also works well with desktop mail clients if the user prefers. That would seem to accommodate the widest range of situations -- all non-OS X desktop and mobile platforms would be covered, and data synchronization would be ubiquitous, but the UI experience on OS X and iPhone would not be compromised.
I imagine that a hosted software solution would be something of a departure from the OmniGroup's standard software, but I would be willing to pay a monthly or yearly subscription for this sort of product. A sleek <overused cliche>Web 2.0</overused cliche> product would fit the bill nicely. I'm sure the OmniGroup could do it properly.