If you wanted to replace the headphone jack with your "new thing" the most effective way to do that would have to involve as many audio hardware companies as possible also producing headphones that work with your "new thing". You would want to pre-announce it along with specs and make it an open standard that other companies can utilise without paying royalties.

The GBA still wouldn't have had anywhere near enough market share to pull it off. Apple definitely could've, I think. I haven't followed closely enough, but are other accessory manufacturers able to produce headphones for the new iPhone, or is it completely limited to whatever Apple release?