As long as you can shard (across multiple instances, or even within same instance, to avoid B-Tree latching), 1B+ rows within MySQL is piece of cake.
Also, MySQL* is getting LSM-Tree support lately, which makes high performance data ingestion combined with OLTP workload quite feasible.
* https://github.com/facebook/mysql-5.6/tree/webscalesql-5.6.2...