A basic starting city, at the previous age for the new one, with all expansions released up to this previous age unlocked and placed, with a starting amount of resources (coins, supplies, diamonds, goods, special goods, BPs, unattached troops, ...) equivalent to the basic starting city at Stone Age would be fine. If all previous era's research tree is already done each player could transform the city to his/her play style quickly and then kick off at new age by unlocking the first research tech. This solution would be faster than waiting for months to finish pending research to be able to unlock the new era (depending where the player is at the Research Tree when new era is ready at Beta).
The only thing I see missing is the GBs at the level the player would have developed through time at that era. Maybe Inno could program at that world x to have available to the tester an option to select X number of GBs, each at a level YY, to be placed at the city when starting the world. After that, each additional GB (X+1) would be built by the player the usual way.
That would provide a large number of players able to test a new age in Beta instead to only the smaller group that happen to be at the end of the research tree at the time when a new era is released.
----
A second option I see is for Inno to design a few starting cities, and give the player the option to select the one closer to his/her playing style. These cities maybe selected from the live servers, or designed for playing styles like:
- Aggressive Battle / Attack / Plunder players
- Passive Producers / Merchant type players
- Balanced Aggressive/Passive players
- Mostly Terrace Farms / Shrines cities
- Others?
