First, let me remind you all that the charter for this list really doesn't permit griping about companies that have been gone for many years. It's a support list, where users of Frontier ask for help from other users. It's unmoderated, but if the gripes of the past come back to haunt us it will become a moderated list, so please stay on-topic. ;-)
So here are the choices that exist today for people using Frontier or the OPML Editor, as I see it.
1. Don't update your Mac to Mavericks. That's what I'm doing. I depend on the OPML Editor for my daily work. I'm concerned that one of Apple's automatic updates will update me to Mavericks since it's a free release. So I'm avoiding those as well.
2. Run the Windows version of the OPML Editor in VMWare or Parallels.
3. Run the Windows version of the OPML Editor on Linux using Wine.
The Windows version seems to be in decent shape for the foreseeable future.
About doing the work to get the codebase to run under Mavericks, one of the original guys tried to do this, but gave up. Too much had changed. The GDI on the Mac has changed, as has the networking model. We had been using deprecated APIs for a long time. They finally pulled the plug on them.
However -- if you want to pursue that approach, it's best to use the tools available like Kickstarter or Indiegogo and let's pool the money and then try to attract the developers. I would say a bounty of $25K would probably get some interest. But we'd have to be careful to employ someone who has the programming ability to deliver. There are a lot of people floating around who say they're gutsy programmers, who would probably not be able to do this port. Frontier is a pretty complex piece of software internally. But it is organized in layers, so the work probably is fairly compartmentalized.
Dave