Add a new type of related issue: "exclusive"
That is, if resolving one issue conflicts with another issue (or several) and vice versa.
A bit like blocking/blocked by, but both issues are blocking/blocked by each other (not a blocked-blocked by pair).
As a bonus, if one of the associated exclusive issues are resolved (or in progress?), all the others are set to "rejected" automatically (with a comment like "rejected by exclusive issue #nnn).