Also, it may not be necessary to have a TimeStamp object in ZODB 4. There are three uses for the timestamp: tracking how recently an object was used for cache evication, providing a last modified time to users, and as a simple version number.
In ZODB 4, the cache eviction may be done quite differently. The version number may be a simple int.
WRT RAM usage, a Python int is no smaller than a TimeStamp object. An int pickle is likely much smaller, though.
The last mod time will not be provided for each object; instead, users will need to define this themselves if they care about it. If they define it themselves, they'd probably use a DateTime object, but we'd care much less about how small it is.
Unclear that we'd care less, if the catalog remains full of DateTime objects, and Fred is channeling more faithfully than the rest of us <wink>.