I recently discovered something accidentally in Power BI that might be useful. My colleague Mihaly found a similar technique by accident too a day or so before, so I thought I’d share what we found.
We ended up creating a line chart with conditionally formatted markers :

It’s really quite simple to achieve. Here’s my simple data set:

First I create a simple column chart:

Then in the formatting options, set up conditional formatting on the bars:

Which then results in this:

At that point simple switch the visual to a line chart:

You can also use the format painter to copy apply from one chart to another.
It’s very unlikely that this is supported by Power BI, so use in the knowledge that is might stop working.