Carefully considered suggestions for revision of the TNIV are now being accepted at a service posted on the TNIV Truth blog. If you wish to pass Go and not collect $200 (!), you can access the webpage directly for entering your suggestions by clicking here. Please read further instructions in a TNIV Truth post.
UPDATE: Before you post, check to see if the TNIV team has already addressed a concern that you have about a verse or a more general pattern of translation, such as their use of “brothers and sisters” for when Greek adelphoi refers to both male and female Christians. If they have addressed the issue on the TNIV website, do not submit your suggestion for a verse. The CBT (Committee on Bible Translation) is extremely busy and does not have time to sort through suggestions for TNIV revisions which they have already considered.