User-821857111 posted
No. Changes to WebMatrix will not affect SimpleMembershipProvider, which is part of the ASP.NET Web Pages framerwork. That is still on version 2. I haven't heard of any plans to release a version 3 yet.
ExtendedMembershipProvider is just a base class that you need to inherit from if you want to create your own provider that implements ExtendedMembershipProvider features. SimpleMembershipProvider is an example of doing that.
You can create your own provider. The simplest way to do that would be to basically copy and paste the source for SimpleMembershipProvider
and change the name, and any SQL that won't float with MySQL.