I think anyone can be sub-20, the first recorded 3x3 WR was 22.95 sec, and just based off of new cube technology alone anyone can achieve this time. A lot can be sub-15 if they learn full OLL. I also think it's possible for a large amount to become sub-10, or at least get a sub-10 single in their lifetime. There are now over 1200 entries in WCA under 3x3 for PB singles before a sub-10 shows up (1221 to be exact). Right now there are 241 people with an official sub-10 average, and 9290 with an official sub-20 average. That's amazing!