If I attack with a character that is upgraded with an anticipation engine and the first card flipped is an action that untaps my attacking character, such as Start Your Engines in a cars deck, does my character still count as attacking? Does it still flip battlecards for attack? Does my opponent need to wait for me to attack with the same, or another, character?

Another similar confluence of mechanics would be OPBL flipping a swap missions during attack and untapping. I know the effects and triggers are at slightly different points in the attack but the result is broadly the same; an attacker that hasnt tapped out that round.
Is this intended?

Changing the tapped/untapped status of a character does not affect whether it is attacking or not. At the end of that attack, if your opponent has any untapped characters, your turn ends. Otherwise, continue attacking with any of your untapped characters.

Source: Wizards of the Coast (2019-09-06)    【Link to Ruling】

Tags: Attacking