The BIDS specification can be extended in a backwards compatible way and will evolve over time. This is accomplished with BIDS Extension Proposals (BEPs), which are community-driven processes (see BEP guidelines Google Doc).
On the BIDS homepage you can find a list of extension protocols that are currently being worked on.
All changes that are not backwards compatible with the current BIDS
specification will be implemented in BIDS
2.0. See the corresponding