This is a brief issue to possibly start discussion and so we do not forget.
Attn @tsalo @satra

ATM, to accomplish the job, many BEPs need to introduce changes to

• BIDS common principles (e.g. "Indexable metadata" of BEP001)
• add new "entities" (_keys) (Add "part" entity for magnitude and phase data #367).

Quite often those changes are of interest for multiple BEPs, (e.g. _part for BEP001 (multiple contrasts) and BEP004 (SWI)), or even could be argued to be applicable to existing "raw" BIDS itself (e.g. bids dataset provenance, #369).

But being introduced in dedicated specialized BEPs they

• lack proper review by wider BIDS community, and thus have more potential to introduce conceptual inconsistencies within BIDS
• make BEPs development/review/acceptance stagnate
• make more difficult for support tools (validator, pybids) to review/adopt them

I would propose or us to

• improve contributing guide, in particular for BEPs, to RECOMMEND (if not REQUIRE) introducing any such changes as separate PRs against BIDS, with references to existing (or proposed) BEPs
• work between/with existing BEPs to identify such atomic changes and propose them as separate PRs
• for PRs add labels for each BEP (BEP001, ...) so we could see which PRs would be of use for which PR