New releases of the SSIS+ Suite are always backward compatible. We will provide support for all versions of SQL Server that are still supported by Microsoft at the time the new SSIS+ version is released. Therefore, it is not necessary to run different versions of SSIS+ side-by-side.
If you are concerned about introducing changes to packages that have been running successfully by upgrading to a new version of SSIS+, we understand your concern. However, in order to support different versions of SSIS+ running side-by-side on the same server, we would need to save version information in each package so that the desired version of SSIS+ would be used for each individual package. The downside of doing this would be that, when you want to upgrade your packages to use a newer version of the SSIS+ suite, you would need to change each package to update the version information saved in the package to the new version.
With the way it works now, you don't need to update your packages when you upgrade to newer versions of the SSIS+ Suite. The packages just work with the new version of SSIS+.
To lessen any concerns you may have about migrating all of your packages to the new version of SSIS+, we recommend that you test all of your packages with the new version of SSIS+ in a staging environment before moving them to production.