Make open more of API for compile-time stage
I think possibilities of the compile-time stage are underestimated by the community and by Microsoft itself.
For example, see: http://omari-o.blogspot.com/2009/09/aspnet-white-space-cleaning-with-no.html
Reflection was used in this cool solution, because there isn't 'official' way to do some stuff. I think it can be turned into the excellent unique advantage of ASP.NET. Don't you think so?
ControlBuilderInterceptor added in .NET 4.5
We added the ControlBuilderInterceptor class in ASP.NET 4.5 to allow customization of any code generated from an ASPX/ASCX file at runtime before it is compiled. This basically gives you access to do what a custom ControlBuilder would be able to do but for any control (or even the page itself).
Marco Alves commented
I would love that feature in ASP.NET!
Damian Edwards commented
We are investigating ways we can open up parts of the compilation system in Web Forms to enable more advanced scenarios like this more easily. Thanks for the feedback.
ControlBuilders infrastructure is great but need to be more flexible and consistent