Absolutely brilliant!
This brings FoG2 to the same level of FoG on this matter and now offers that same functionality, especially where we get the era overlap between the end of the Ancient era and the start of the Medieval. This makes FoG2/Medieval so much better.
You can have a look at this awesome game here... Yes, I'm a fanboi, I admit it.
https://store.steampowered.com/app/1368870/Field_of_Glory_II_Medieval/Slitherine Press Release
Field of Glory II Medieval - Time Warp free Add-On
A new add-on for Field of Glory II: Medieval has arrived and it will allow everyone to create their own “Time Warp” battles. This new feature allows custom battles to be fought between armies from the Ancient period and Medieval armies (or vice versa). It will be possible to create an infinite number of customized "what-if" battle situations, which can be played against the AI or in multiplayer. If you ever wanted to know how the Normans would have fared against Augustus’s legions, or the Assyrians against the Teutonic Knights, now is your chance. You can play these battles and more using the new “Time Warp” feature. To set up an anachronistic matchup, you will need to click on the “Select another module” button (in the Custom Battle setup screen) and turn off the Date and Geographical filters in the Enemy Army List selection panel.
The “Time Warp” add on is totally free and will allow all Field of Glory II: Medieval players to setup and fight single player and multiplayer games using any Medieval army and any FOG II “Ancient” army, from any DLC published for FOG II “Ancient”.
Please note that currently, it will not be possible to create a fight between two Ancient armies, nor to use the FOG II “Ancient” client to play against “Medieval” armies.