Personally, I don't start worrying about it until it actually becomes a problem (i.e. when an alter actually takes more than a few seconds to run). At which point it's easy to migrate to using pt-online-schema-change.
Then again, I do most of my DB maintenance manually (I have DBA experience), so while I do use Django in production, I have less need to rely on generic automation tools.
Or use PostgreSQL, Oracle, MSSQL, or... lots of options there.
[EDIT] As a final thought on the topic, never be afraid of making schema changes, even in MySQL. It may require a bit more work to implement, but there are a bevy of solutions (most of which can be automated) which can limit or eliminate the "pain" caused by such alters.
Then again, I do most of my DB maintenance manually (I have DBA experience), so while I do use Django in production, I have less need to rely on generic automation tools.
Or use PostgreSQL, Oracle, MSSQL, or... lots of options there.
[EDIT] As a final thought on the topic, never be afraid of making schema changes, even in MySQL. It may require a bit more work to implement, but there are a bevy of solutions (most of which can be automated) which can limit or eliminate the "pain" caused by such alters.