If everything is behind an ORM, have you considered trying out PostgreSQL w/ the MySQL FDW? pgsql 10's improvements to FDW's make it a truly viable option.
Also to clarify: I'm just saying this as pgsql seems to handle queries that involve disk access and large datasets much better. I have found that as long as your hot dataset fits into the innodb buffer pool and/or you're doing only key lookups (e.g.: select * from tbl where pk=1;) MySQL is most certainly faster for real-world usage. If you're pulling and sorting/filtering millions (or billions) of rows per query, I find that pgsql stands up extremely well to that. Even in a single huge server setup.
Also a semi-unrelated ditty, but as someone who has to run migrations on pretty big (100m rows) tables, ALTER TABLE LOCK=NONE ALGORITM=INPLACE is pretty great (here's a table of what you can user per-situation https://dev.mysql.com/doc/refman/5.6/en/innodb-create-index-...)
If you made it this far in my comment you'll probably realize I didn't grasp the article well. I just re-read it and tl;dr, MyRocks works well (as expected) with datasets that don't fit into the innodb buffer pool. :)