That's the part that surprised me as well; it doesn't seem like a field that should be eligible for anything other than an exact match. I am unable to conceive of a use case for pattern matching account IDs.
Given the way these IaaSs' distributed KV stores all manage writes (i.e. by having a cluster of transactor nodes that per-key write-linearization responsibility for parts of the keyspace is sharded across — such that writes are fanned out to a particular designated transactor-node given the key's hash-slot), a very large S3 user, generating an extremely high level of metadata-update concurrency against a bucket, could very likely write-contend that bucket's metadata / have a "hot" bucket-metadata key; experience low perf due to that; and solve that by sharding the bucket (swapping one too-hot metadata key for N somewhat-hot metadata keys.)
I want to give an intuition-building example here, of an IaaS feature that wouldn't exist / wouldn't be exposed to the user if not for object-storage buckets being metadata-write-contended at scale. I'm not very familiar with the AWS ecosystem, though, so I'm not sure what the good example is for AWS. What I do know is GCP, so here's a GCP example: Google Cloud Dataflow allows you to set a temporary workspace GCS bucket on a per-job basis (gcsTempLocation). And, IIRC, Google's Cloud Architects advise to not have a bunch of active Dataflow jobs sharing the same gcsTempLocation — regardless of whether they use distinct key prefixes to namespace the temp files. Given that each job would be doing a lot of little serial updates to the temp bucket — and given that Dataflow jobs can each be highly internally concurrent — you're already potentially putting out O(N^2) ~concurrent updates to that bucket. You really don't want to make it O(N^3).
filter = property, operand, value
Sharding on account ID might make sense if someone has a large number of them, but that would not necessitate wildcard matching.
Either you bucket by an internal ID and give the user a hash, or you give the user an ID and bucket by your internal hash.
Users have no business knowing your sharding scheme.
Odds are that an account wildcard match like 676363687* will just match a few hundred entirely random AWS accounts.
Honestly, wouldn't surprise me that much if they were willing to accommodate this if for sufficiently large accounts. It'd still pretty sketchy to design your access control around, but it wouldn't be unrealistic.