As OLX and other ecommerce established brands uses, it would be of huge interest to develope a plug-in or more, to integrate machine learning for features like:
1- Site security(identify unlawfully behaviour, identify and block or report malicious content. E.g. how you identify an user which to escape the payment creates another account, another phone nr and reposts for free? Must be a way to analyze text and identify similar listings and block it)
2- Product recommendation
3- price suggestion

And others.

ML is too advanced and complicated to pack as a plugin. There are many elements to it that require technical knowledge to implement from infrastructure to coding to data and language processing.

Best to implement as custom work as each site is different and the end ML solution would differentiate one platform from the other in the features and services provided.

Not saying it's not possible, just too complex to build into and deliver as a plugin for a variety of use cases / user levels.

Well, advanced and complicated makes the difference, just ask the right price

just ask the right price

Well yeah, anything is possible for the right price! However, customization triumphs mainline as that's the difference between standing out and making it, and being like the rest ie. just another classifieds site.

Plugins can only take you so far.