So long as you are confident you can retain a clear editorial identity I think this could work fine.
By editorial identity, I mean that the non-Traveller material needs to fit in with the Traveller tone of the magazine. For example transhumanist and cyberpunk might not be suitable. However games such as Stars Without Numbers and Diaspora have a similar kidn of feel to raveller and migth fit in well.
I think there's no harm including a few select articles of this kind on a trial basis and see how your readers respond. You might even find yourself acquiring a new community of readers from fans of these games, if they see similar synergies between the Traveller material in the magazine and their own games.
Check out StarBase
, the open source science fiction campaign mapping application.