legendary at 777 (instead of 775) would be cool.
Do you mean the merit count or activity? Merit requirement for legendary rank is 1000 and the activity period could fall anywhere between 775 and 1030 and is random for each user.
I think it would be great if the ranking system was tagged on angel numbers instead of round up numbers.
There are many other unique number combination, buy I think the system is fine as it is. Users can always save their memorable merit records (like 777) as they grow their accounts.