Allow a "never match with" list but allow for "matches against".
Alot of people say that a block list that disallows you from being matched with players that you've blocked can be abused. Agreed, even though I'd like such a system to be implemented.
However, it would NOT be open for abuse if the system allows you to be matched AGAINST people you've blocked, just not put them on your team. This is not abusable since enemy team composition is essentially unchanged from live. All that changes is that people on your block list is not available to be placed on your team.
This can't be abused by say, blocking everyone below you, since there's always going to be someone worse than you. It can't be abused by blocking those above you, since blocking those above you means that your team is just worse on average.