Is there a way to process points in a Wrangle sequentially, as opposed in parallel?

Run over your points in a 'for' loop in detail mode.

I dont think there is any way to truly sequentially process geometry elements within VEX at least not in an intuitive sense for cases that such processing would be necessary if you expect each iteration to result in a modified geometry that later iterations can access

While you can run over elements using for loop in a Detail wrangle, you'll need to keep in mind that all functions like set*attrib() will defer setting of the attribute and also all geometry sampling functions like point(), prim(), ... Will only be able to sample one of the input geometries, not the currently modified one

So even in such loop you will need to keep track of previous element's modified attributes using variables if you want to use them for values of later processed elements, etc..

On the attribute wrangle node, right click, click on allow editing on contents, then jump inside, click on the core node inside, below you will see an enable multithreading button, you can turn that off, then you will have almost sequential evaluation.

but as mister slanic said, you won't be able to access previous iteration data like this, to do that you will have to build a for loop kernel on yourself in detail mode and manage the processed element data.