If you have written add-ins for Visual Studio that deal with Windows Forms, and have tried to make it work with HTML/ASP.NET pages and controls, you already know that, well, it is quite difficult if not impossible because:

1) HTML pages contain HTML controls, while ASP.NET pages can contain HTML controls or ASP.NET controls

2) VS 2008 changed the internal designer arquitecture for HTML/ASP.NET

3) VS doesn’t expose good extensibility points for add-ins (and maybe not even for packages)

There were lots of questions in the forums about all this and I wrote a post a year ago:

The (lack of) IDesignerHost in Visual Studio 2008 (Orcas) ASP.NET Web pages
https://www.visualstudioextensibility.com/2007/12/18/the-lack-of-idesignerhost-in-visual-studio-2008-orcas-asp-net-web-pages

OK, now the good news: Mikhail Arkhipov, the person within the Visual Studio team that can change this (I exhanged e-mails about this in the past) has just posted this in his blog:

What kind of extensibility would you like to see in HTML/ASPX editor?
http://blogs.msdn.com/mikhailarkhipov/archive/2009/01/19/what-kind-of-extensibility-would-you-like-to-see-in-html-aspx-editor.aspx

So, Microsoft is listening. It is our chance to speak 🙂

I will write Mikhail in a couple of days with a detailed explanation and sample of what I would like to do from within an add-in.