support is a key differentiating factor in TideSDK vs anything in future that may be competitive
I strongly feel that TideSDK should not go the route of using its own proprietary web framework. It bloats the distribution and installation size, requires development and support of the framework, and is just plain unnecessary when there are web frameworks that ship with each major desktop OS. It is only with mass adoption of a tool that distributing a framework doesn't really matter, but not even Silverlight, AIR, .NET, etc. have what I would consider mass adoption. So chances are your app may be the only app a user has installed on their system that requires a proprietary TideSDK framework. So why do it?
Here would be my suggestion instead. Go the phonegap route and just embed a webview from an existing installed web framework and build off of that. This would keep most app redistributables under 5MB!Mac OS X
This one would be pretty straight forward as well. Ubuntu (and Linux Mint), arguably the most used end-user distributions of Linux worldwide, have been shipping the XULRunner runtime with their OS for several years now. And for the distributions that don't ship with XULRunner, installation is very straight forward for most *nix folk (sudo apt-get install xulrunner).
"Trident Shell" - IE Framework/Google Chrome Frame/XUL Runner
Dealing with Windows is a little harder and certainly deserves further discussion, but I think there are good ways of handling this OS without having to distribute a web framework. Windows Forms applications allow you to embed a web view into the app that use IE. Check out these examples:
Using IE is certainly not ideal I know, but there are workarounds. TideSDK could search to see if either Chrome or Firefox is already installed on the target OS and use those frameworks instead. "Google Chrome Frame"(https://developers.google.com/chrome/chrome-frame/) does this quite painlessly for IE 6-9 users as a simply browser plugin and perhaps something similar exists (or could be built) for using an installed Firefox framework. And it could degrade nicely by using the developer's preferred framework and then only using IE as a backup.
In addition, Windows 8 plans on shipping with a great web platform called Windows Runtime (WinRT). It should also be noted that if a developer plans on creating any app for Windows 8 on ARM, that WinRT is required and metro-style apps distribution is a requirement!
Well if you made it this far and I haven't lost you, here is another idea. Why not join development efforts with Apache Cordova and the PhoneGap team? Getting acceptance and dev support from them in the beginning might help to spread adoption of a phonegap-desktop framework and perhaps even become apart of the powerful PhoneGap:Build tool.