I have a suggestion. What about using split?
So your shortcode could be something like:
{{ .Get "name" | markdownify }}
{{ $aliases := split (.Get "aliases") "," }}
<ul>
{{ range $aliases }}
<li>{{ . }}</li>
{{ end }}
</ul>
And be used like:
{{< shortcode
name="Peter Parker"
aliases="Spiderman,Petey">}}