Orochi looked right at Zoro when he was gonna get cut down and Zoro's exact face has been on wanted posters for over two weeks and King is a beast pirate do he has access to wanted posters and could just have easily looked at the wanted posters when Hawkins reported that luffy atgnd his crew were in Wano.
So orochi and king have both seen Zoro's face.
What you are saying is that they are waiting to tell Zoro they killed his father when they see him and Zoro is going to CARE???
And this will somehow matter to the plot .
First off, I know that orochi has seen him.
But what I mean is, they don't know him truely.
What are the odds, that a pregnant woman is send off from wano to the east blue about 20 years ago and that child coming back to wano as a pirate?
And most probably, only a few shimotsuki knew about ushimarus son, aka zoro, because ushimaru and the other daimyos were about to revolt, so he most likely hadn't told anybody about a woman who was pregnant with his child and send them to shimotsuki village in the east blue, so that his child would be safe.
So they didn't realize it at this point.
All of that is my theory, I'm not stating anything as a fact (just to be clear).
And zoro is not going to care, which I pointed out by saying "avenging". You see the " "?
Just that he will defeat them.
And what this has to do with plot relevance? Well, you get to know the background of the first mate of luffy. I don't know about anybody else but I'm interested in it 🤷♂️
+ this would fit with yasuie shimotsuki's plotline and aftermath.
Depending on oda, there could be a few other points which would be relevant.
For example, zoro was interested in the nidai kitetsu. What if that was the sword of his father and the one whom tenguyama awaits is zoro (and not the kouzikis. He never said for whom he waited).
So at the end, zoro will get a justification to get a stronger sword than his current one.
Considering his personality, he would not switch it just because it is a better grade and letting the sandai kitetsu break would be pretty lame at this point of the story.
And so on.
Of course, non of that has to happen 🤷♂️