This is downright terrifying. A major escalation of the blackout and deleting your content - with the help of european law - is a nice response to that, if they do not step back. This is perhaps the most extreme measure to be taken, short of destroying the data center itself. An emptied reddit history is a massive loss of knowledge and perhaps questionably damaging for the outside world.
According to WP: The GDPR also applies to data controllers and processors outside of the European Economic Area (EEA) if they are engaged in the "offering of goods or services" (regardless of whether a payment is required) to data subjects within the EEA, or are monitoring the behaviour of data subjects within the EEA (Article 3(2)). The regulation applies regardless of where the processing takes place.
It would leave them open to potentially devastating legal consequences if an affected EU citizen can prove in court that reddit makes money of his content, which he deleted. Also the "right to be forgotten" as in the GDPR formulated would be violated.
IF reddit really goes that way, they'd have to anonymize at least the usernames. Which would make it extremely hard to prove that something is "your content" and not someone elses.