A:  The CURRENT uncertainty in parallax measurements
            by Gaia is, very roughly, about 0.2 mas.


      If we adopt the very rough rule that one should
            only use parallax values which are at least
            10 times larger than their uncertainties,

               maximum "good" parallax  ~  10 * 0.2 mas

                                        ~   2 mas

            So

               maximum "good" distance  ~  500 pc


  A:  The expected FINAL uncertainty in parallax measurements
            by Gaia is, for bright stars, about 0.01 mas = 10 micro-arcsec.


               maximum "good" parallax  ~  10 * 0.01 mas

                                        ~   0.1 mas

            So

               maximum "good" distance  ~  10,000 pc