Presumably it was at least considered. I would guess that the negatives would be taking more disk space (and potentially imposing greater IO concurrency though

Presumably it was at least considered. I would guess that the negatives would be taking more disk space (and potentially imposing greater IO concurrency though that probably isn't a great issue with modern storage systems), and it being more complex (if not in the core design, then in having extra edge cases to make sure are all covered). Other databases do do similar to what you suggest, though obviously the trade-offs will differ because of other different internals and product priorities, so it would have been thought about. For instance MS SQL Server has multiple “virtual logs” in its log files, for at least some overlapping reasons.