The current state of Classic Era’s is this;
Several servers have been merged together / cross realm activity has been enabled - which is great! But seeing the amount of people (which isn’t a lot) I would recommend that you merge all servers together / enable cross realm for all servers.
There are a handful of people on each merged layer of realms, given you enable all servers to interact with each other it might almost resemble a proper active server which could have a stable economy, auction house, guilds and dungeon groups / raids.
With that being said, PvP / PvE and RP servers should still be held seperate.
edit; Let us hope blizzard holds by their promise of this thread, before it’s too late for Classic Era realms to recover.
“and we’ll continue to monitor and consider further connections in the future.”