I doubt that this would be possible.
A solution consists of a number of completely different file types, each in their own format, with a different purpose:
- The solution file is in a legacy (non-XML) text format and informs your IDE (typically Visual Studio) about all the different projects that are part of the solution, as well as pointing it to other files relating to the solution such as test run configuration settings.
- Project files these days are XML build files that inform MSBuild what source files are to be built, and how.
- Source files contain code of an arbitrary programming language.
- Other files a project can also have any other arbitrary text or binary files. (For example, embedded resource images.)
So there we have at least four different file formats: non-XML text, XML, plaintext, and binary.
Perhaps the only way that you could achieve the combination of all these disparate file types into a single file would be to have some mechanism to magically extract all of the separate files out from your single file, present them to the development and build tools as if everything were normal, and then magically re-combine them back into the single file after.
That would be roughly equivalent to taking the entire solution directory and running it through WinZip to produce a single file (a compressed file, to boot!) though perhaps witha more seamless integration via a Visual Studio Add-In.