phew, theoretically silverstripe is divided into a core framework (sapphire), and an UI-layer building on top of it (jsparty/cms). as we're developing the two pretty much in parallel, the ties and interdependencies are stronger than we might like in some areas.
meaning: you could use the controller/model part with custom rendering, but you'd still have to worry about things like form-rendering/handling which is naturally tied between the layers.
a .NET-frontend would certainly be an interesting thing to see, but i doubt that using a script-based php-framework tailored towards CMS outweighs the advantages of having a native .NET-MVC-framework (quick googling got me: sprint.NET, maverick.NET, openSEAL)
I appreciate the candid response. I havea dotnet app and desire an api based content management system.
There are two native dotnet Open Source CMS projects that look promising:
Both have their own merits. The former being a mature CMS platform with vibrant community and an API, the latter being no more than a provider pattern based object model with significant capabilities and limitless flexibility (its just a content domain model with configurable providers)
I've been experimenting with both and am currently using Eucalypto because of stringent, dynamic and complex url rules that my website has.