I've been tinkering with this problem. It's kind of frustrating not having a right solution for this.

After trying and failing to the last solution published by Hraban on 2018-02-12, I tried to implement my own approach, from the other way around, I mean: not trying to implement notes as marginal material, but to implement the marginalia as some type of notes. A different type, apart from footnotes, with their own counter, etc.

Below, a MWE, with some caveats:.

1. This is a poor quality hack. I'm not a developer.

2. If notes are too long, they clash with each other. I tried to understand the options that would allow me to move them up or down, according to the Wiki (https://wiki.contextgarden.net/Command/inmargin), but they don't seem to do anything, or I don't understand how to work with them. But if there is actually a way to manually instruct \inmargin to move up or down, it should be easy to make it work as an optional third argument, for example.

3. The counter introduces some horizontal space that I cant manage to remove except by introducing manual negative \hspace. The MWE doesn't include that space, to display the isse. 

4.  There are probably a ton of issues I have not thought about, but this seems to work for this project I'm working on, at least.

%%%%%%%%%%% Start MWE

\setuplayout[
    topspace=0.722in,
    header=0.311in,
    footer=0.622in,
    width=4.211in,
    height=9.622in,
    backspace=1.311in,
    rightmargin=1.8in,
    margindistance=24pt
]
\definecounter[marginales][way=bytext,prefix=no]
\def\romanMarginales{\convertnumber{r}{\rawcountervalue[marginales]}}
\def\marginal{\dosingleempty\doMarginal}
\def\doMarginal[#1]#2{%
  \incrementnumber[marginales]
  \iffirstargument
    \high{\romanMarginales}\inouter[#1]{\romanMarginales.\ #2}
  \else
    \high{\romanMarginales}\inouter{\romanMarginales.\ #2}
  \fi
}

\starttext
\dorecurse{6}{\input weisman And so on, and so on\marginal{This is a test, with some words and some more words.}.\par \input thuan\par}
\stoptext

%%%%%%%%%%%%%%% Stop MWE