Another thing to consider is that if a DT1 gains an exclusion that renders them net excluded, it could have far reaching effects, triggering other exclusions or inclusions, possibly even resulting in some kind of endless cycle that might break the trust system 
Let's say 2 DT1-users have no inclusions from other DT1-members, but they exclude each other. In the current system, they both have DT1 Strength (-1). Following GazetaBitcoin's suggestion, their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded.Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. Since their exclusion becomes invalid when they're excluded, the other user is no longer excluded and reaches DT1 Strength (0) again. Being back on DT1 means their exclusions becomes valid again, and they're excluded. .......