Version restrictions are very strict.

[ghost]

Backstage has many very strict dependencies in its gemfile, for example, backstage depends on thor 0.14.6 exactly. This makes it very difficult to use backstage with any reasonably sized app.

[bbrowning]

Backstage is not meant to be used inside your application; it deploys as its own application. So, the versions backstage uses shouldn't impact the versions of gems your application can use.