I'm running EV10.4 and SQL 2008 R2 and planning to upgrade to 11 and SQL 2012, my first step is to upgrade the DB, is there any particular issue to be considered to run an upgrade in place of the SQL server from 2008 to 2012 ?
No issues from the EV side really. Just consider the pros and cons from the SQL side. Have a look on this article: https://logicalread.com/sql-server-2012-in-place-upgrade-w02/#.Wc6BTNMjE6g
Also, I would suggest to take a backup of all EV databases and stop the EV services before starting the SQL upgrade.