Would something like max_logical_wal_senders also be needed for your purpose? Otherwise, logical replication connections could exhaust max_wal_senders and prevent physical replication connections from being established.
That said, adding two separate GUC parameters (i.e., max_logical_replication_slots and max_logical_wal_senders) for this purpose doesn't seem like a great solution, though...
For my purpose, it doesn't actually seem that I would need max_logical_wal_senders to limit WAL senders. Since each logical connection always requires a logical replication slot, the actual number of active logical connections (and logical WAL senders) would ultimately be bounded by max_logical_replication_slots. My main concern is therefore slot exhaustion rather than the WAL sender limit.
