Think about a generic cluster.
Usually we use the same item name/key for each node on cluster, basically the same template.

Then to monitor a cluster status we need a trigger with expression like:

{node1:key.func()}=0 and {node2:key.func()}=0 ... and {nodeX:key.func()}=0 

usually 2 nodes are used, but it should allow to create more than with 2.

How to configure such a trigger? Especially that currently for many resources we use LLD to create items.
Currently there no way to do it and it's a limitation.
Create triggers manually, using LLD generated items - is not a solution.

I could not imagine for now how it may look like, but some nice design could be found, I believe.
Ideally there should be a way how to define that some hosts have relations - they are nodes of a cluster. Then trigger prototype could have an attribute that instructs to try to find similar items on hosts of the cluster and try to combine trigger expression as configured.