There can cooperatively be multiple implementations that have different developers (as long as they coordinate with other implementations), and written in different code , different languages, and with different features that don't break consensus.
Which won't happen if one group (such as Bitcoin Classic) decides that the other group (Bitcoin Core) are not the right people to be doing the job (which is exactly what is going on).
Gavin could fix all of this by simply making a statement that he won't disagree with the Bitcoin Core group (but of course he won't ever make such a statement so we have a stalemate).