VSIX distributed extensions are installed into Visual Studio therefore requiring each developer to have the same version of the extension installed. If one developer upgrades then the build will break for everyone else until they upgrade. It also means that automated builds on a build server will require constant maintenance to install the current version of the extensions (not to mention conflicting versions on different build definitions).
An excellent article by Oren Novotny outlines the solution, to make a change to the project file instructing Visual Studio to look in a local folder in the solution for SDKs first before checking the default machine location.
The folder needs a particular folder structure and naming convention for the above to work.
Follow the steps below to use the extension.
You should notice that the reference path in your project will point to your new local folder.
Now all the developers in your team will pick up the same version of the SDK from the local copy, as will the build server.
If you wish to upgrade, just delete the files from the libs folder, and repeat the above process.
More info and source - https://github.com/MarkerMetro/ExtensionSDKConverter