we can have a slide left and right for each plugin - this generates an infinite list on the side as well
What is this category search box about?
Did you mean the selection next to the search field? I'm trying to keep the interface aligned with the in-app version (still a open PR made by makb). It meant to work as a filter, a user can search a plugin within a category. Is that excessive and need to be removed?
Yes just a search box please. Have a look at what other stores do.
Thanks for your participation!
I see two things in your redesign if I understood correctly.
The first is that you removed the category selection section. It was this way before if you checked my version 1 mockup. But after some discussions, I found that we need a way to filter plugins in categories, so I took what the chrome extension store did - put a category selection on the left side. Maybe we can discuss if there is a better way to do it, but I'm afraid simply removing it won't be the answer.
The second is that you add infinite scroll to the page. I see a lot of websites are doing this, but is this a little excessive for this plugin discovery website? Our number of plugins are limited for now, and it seems that we can only repeat the content has shown before. I don't see why we should do this.
I agree to this. And this is what I wish to achieve.
I tried the interactive prototype. It's quite impressive!
My only comment would be to make it clearer that the search box is a search box. Currently, it looks as an empty text box. To make it clearer, you could add a 
icon and add a default text when the field is empty that says "Search plugins". If you need help finding an icon, just ask me 
Also, I agree with the others that we have to consider mobile devices. The website should be responsive and adapt to improve usability on mobile. That being said, we need to remember what the website is for: searching for plugins for Joplin. I would guess that this is not something that users typically do on mobile, so a mobile responsive website would be a lower priority compared to having a solid "desktop" website.
Thank you for your support! I'll make the search box clearer in the coming week and I'll make the page responsive after I finished the detail page. 
a question... has this already been implemented?
It is still in progress see Coding Phase - Week 8 Report for the current status
would appreciate it if you share your thoughts as well in the related discussion Plugin Website - Joplin Forum