The <<linkappend>> macro has a transition/t8n argument, if you're looking for a fade in. For example:
I spy with my little <<linkappend "eye" t8n>>, a crab rangoon<</linkappend>>.
For a staged reveal, where entire blocks of text don't show up until some period has elapsed, then you probably want to append a <<timed>> macro. For example:
I spy with my little <<linkappend "eye" t8n>>, a crab rangoon\
<<timed 1.2s t8n>>, a gaggle of geese\
<<next>>, an aardvark\
<<next>>, and the world's smallest violin\
<</timed>><</linkappend>>.