A nice idea in principle but the day a QF Captain turns up to support/help a jetstar pilot will be the day hell freezes over I think.
Whilst the same could be said visa versa, I think that the issues at play here effect FO and SO/CFO ranks at the various airlines...
Would a QF FO show up to support his colleagues from other airlines and his own career progression? Damn straight!!! And if this effects you, then you should show up as well!