For me, 4l.org acronyms sell fairly well with a little outbound marketing. However, not all letters are equal. I've found the following to be most popular to endusers who want acronyms: A B C D E G H L M N P R S T.
I had to pay to find that out though, by registering many 4l.orgs that I couldn't sell. Overall, I made money, but not a huge amount.
In 2014, I sold 8, average was around 400 USD.
2015: 11, ave: 500 USD.
2016: 14, ave: 500 USD.
2017: 15, ave 550 USD.
Of these sales, about half were caught drops, the other half were from auctions.