After six months of being blocked by someone, I believe there should be a process by which the Blocked can submit a plea to the Blocker to, in good faith, argue for their unblocking.
The Blocked should submit letters from up to three mutuals-in-common certifying the Blocked's good character.
At the time of the Unblock Request Form submission, there can be an option to pull up old, problematic or annoying posts for the Blocked to make redlined corrections for how they would post them if they were created in present day.
After the Blocker reviews the submission, they can choose to
a) throw out the request and maintain the block.
b) offer their own counter-evidence to the Blocked's claim of good character—after this is submitted and reviewed by the Blocked, the Blocked can either surrender and sacrifice their request OR begin the process again with amended claims and recommendation letters from new mutuals-in-common. A counter can only be initiated once. If a resolution is not decided after the Blocked's second submitted claim, the request is thrown out.
c) accept the request and unblock the previously Blocked.
If the Blocker chooses to unblock, there is a firm, one month no-block period where the (ex-)Blocker is prohibited from attempting to re-block the previously blocked user. After one month, they are free to block again.
A re-blocked user must wait a minimum of 365 days before submitting another claim to the same Blocker.
Users who feel they are being constantly pestered by an individual blocked user can submit a claim to Tumblr Support to have the Unblock Request Form permanently deactivated for that blocked user.