Assumption of validity isn't the only path. In Australia there is no assumption of validity; the court essentially re-examines the patent when a suit is brought

Assumption of validity isn't the only path. In Australia there is no assumption of validity; the court essentially re-examines the patent when a suit is brought. This doesn't necessarily increase costs/time either, the Federal Court (has patent jurisdiction in Australia) exercises pretty decent case management to ensure that frivolous suits are quickly dealt with.