The addition of ticket relationships is very useful for tracing through the tracker.
Here are a few ideas for enhancements to the current implementation:
1.) In the "Related tickets" section, show the current state (Open, Closed, etc.) of the ticket being referenced. This would likely necessitate a one-ticket-per-line arrangement or something else aesthetically and functionally pleasant.
2.) When modifying the relationship, a ticket history entry (with optional comment) could be created. The history entry for the relationship change should be entered for both tickets. Considerations:
3.) One more level of granularity for the relationship type - "Depends On" and "Required By". A ticket X "Depends On" another ticket Y if ticket Y must be implemented before/simultaneously with ticket X. "Required By" is the same relationship viewed from the other side.
I had planned on something like this but wasn't sure when I would start on it. Going to move it to v3.6 mainly because there is only one other feature being added to it.
What I will do is something similar to the ticket tasks like you said, with a way to select the relationship, such as "Depends on", "Required by", or blank for a regular relationship.
For point 3, I forgot to say that the existing relationship of simply "Related To" for similar-but-independent cases should be kept as well.