SQL Cluster with different Edition Is it possible to join new node SQL in Failover cluster with different Edition?
As example:

Cluster Failover running based on SQL Enterprise Evaluation Edition add a new node based on SQL Standard Edition
I've never tried this but I'm reliably informed it is 100% not possible. It is certainly not supported by Microsoft, for good reason, so why would you do it?


  The SQL Server edition you are installing must match across all the
  nodes in a SQL Server failover cluster. When you add a new node to an
  existing SQL Server failover cluster, make sure that you specify that
  the edition matches the edition of the existing failover cluster.


This comes from this MSDN link found almost instantly after a quick web search.

Bear in mind there are a few obvious and not-so-obvious functional reasons why you would not want to failover from Enterprise to Standard as some features are not supported in both.

The idea of a clustered environment should be that you maintain integrity of the database environment upon failover, so why compromise that in any way, whether talking about support or features?