There are arguably three already. War Wagons are essentially tanky cavalry archers. Tatars get fully upgraded cavalry archers with +1/+1 armour. Vietnamese cavalry archers have bonus HP, but since they don’t get Parthian Tactics, they’re not permanently above the usual level of tankiness. (Of course, you might not consider any of these to be “good”.)
I’m guessing Vikings and Malay? Maybe Koreans?
War wagons are the OG tanks of AoE2, although I didn’t consider them for the purposes of this discussion since you’d have to do a lot to a cav archer via civ bonuses to make it very WW-like. But yeah, definitely a strong concept as far as (unique) tanky mobile ranged units are concerned.
You got it! In the past I’d be more reluctant to consider this since even Viking Cavaliers might be a situationally useful option carried by the brute force of their eco, but now that both civs have been buffed in ways that further emphasize infantry and/or archer play, I think this is a more valid consideration. Although Koreans losing cavalier probably wouldn’t hurt their WR much, I don’t propose to make Korean cav even worse. I still like the idea of trading Hussar for Plate Barding so that they’ll have moderately better cavaliers, and about comparable light cav for a lower price tag.