Who's gonna stay in Early Access with me?

Even if it's done in a relatively casual way, the more you play in a given ARPG, the less time it requires for you to reach the level your character was before, or even higher as some leagues/season mechanics make leveling easier or have powerful mechanics.

The first time you create a character in a ARPG, you might be attached to it, but IMO, it's not the same thing as a MMORPG where you put hundreds and hundreds, or even thousands of hours on a single character over the years. I can grow fond of a MMORPG character (moreso in older MMORPG), but I don't feel much for my non-hardcore ARPG characters, maybe because I'm in full leagues/seasonal play mode.

Anyway, personal opinion aside: Some people do play standard league/seasons characters, and you won't be alone if you play a standard character, but most players will start new characters every league. As for the EA League (or leagues) come release, that league will probably end up being a broken mess with items no longer working properly, or stuff like that, so it might not be very populated. Being an older, and no longer supported league, it might not even receive any of the usual permanent updates to the Standard league.

I could be wrong, but I seriously doubt it's going to have an active playerbase or economy.

I would only if they fixed performance problems and their game engine. Don't want to cook my rig for an EA game.

About to hit level 99 and pushing to 100. No, I won't be staying in EA League.

Very few people will stay in the current league once it shifts to standard and all of this new content everyone is waiting for gets released. The economy in the current league is already dead so hopes it remains steady when another league comes out as well let alone right now are very low probability.