I have checked with both Greek versions that I possess, and a few
5 For all must carry their own loads. NRSV
5 For each one shall bear his own load. NAS
5 For every man shall bear his own burden. KJV
5 For each man will have to bear his own load. RSV
5 Denn ein jeder wird seine eigene Last tragen. LUTH
5 car chacun portera son propre fardeau. LSV
5 Denn jeder wird seine eigene Buerde zu tragen haben. EIN
NIV seems to be the only one which uses a subjunctive. However, the RSV,
NRSV and EIN translate as imperative, and the "shall" instead of "will" in
NAS and KJV implies an imperative mood. So perhaps there is some
justification for tinkering with the mood. I suspect the NIV is actually
implying imperative rather than subjunctive, in any case - English is very
imprecise in this area.
Hope this helps.