While I'd love to see more content for Rome 2, it seems unlikely at this point.
The two unknown Steam database entries have been there for years and are most likely something to do with testing I would think.
There's also the matter of finite resources and manpower.
CA already has Three Kingdoms DLC, Warhammer 2 DLC, Warhammer 3, Troy, and probably something from the team that made Alien Isolation, and whatever the next Historical title will be is also probably in early stages as they seem to like to overlap. That doesn't leave much spare capacity to be also making DLC for a third game (Rome 2,) especially when the two teams we know make DLC (Historical New Content and Fantasy New Content) are already known to be working on DLC for Three Kingdoms and Warhammer 2 respectively.
If OP could provide sources for this rumour I'd be willing to reconsider. But as it stands I don't believe it's likely that CA is working on Rome 2 DLC.