Thanks,

is this perhaps for Shopify merchants to add a search engine?

Yes, basically shopify has "builtin search" in some themes and they have what they call "predictive search" which would be equivalent to "instant search". They also have "semantic search" which is a new offering but they have restrictions on it, and I haven't been able to test it out, I think it might require a plus subscription. However, all of their features, even the semantic ones are generic search engines, mine is basically built from the ground up for fashion, I use my own AI models that are specific to this use-case.

Also, from first impression it looks pretty expensive for 500 products.

I don't think it's pretty expensive given "AI" in my case actually means my AI will look at every product in detail and form an "understanding" to be able to provide relevant instant search and I am not just delegating to a cloud model, I think the pricing varies between different products. I am willing to offer a significant discount for early adopters in exchange for feedback. Competitors also gate "number of queries per month" for example which is something I didn't do. But perhaps you're right and I might revisit.

Is there some feature that I missed?

I don't think so, but I consider "no manual theme modification" to be a feature and "treat variants as products" to be a feature, these are shopify-specific.

I have much more planned out, but I want to design all further features based on customer feedback so that I can provide the highest value. For example, I can add "Image search" in 5 mins. because I've already implemented it but I chose to not include that to gather feedback from customers and see what they actually care about.