Hello,
between problems solved in upcoming 4.1.3 release I see this:

Lost Connection After Host Deploy when 4.1.3 Host Added to 4.1.2 Engine
tracked by
https://bugzilla.redhat.com/show_bug.cgi?id=1459484

As a matter of principle I would prefer to force that an engine version must be greater or equal than all the hosts it is intended to manage.
I don't find safe to allow this and probably unnecessary maintenance work... what do you think?

For example if you go here:
http://www.vmware.com/resources/compatibility/sim/interop_matrix.php#interop&1=&2=

you can see that:
- a vCenter Server 5.0U3 cannot manage an ESXi 5.1 host
- a vCenter Server 5.1U3 cannot manage an ESXi 6.0 host
- a vCenter Server 6.0U3 cannot manage an ESXi 6.5 host

In my opinion an administrator of the virtual infrastructure doesn't expect to be able to manage newer versions' hosts with older engines... and probably he/she doesn't feel this feature as a value added.

Just my thoughts.
Cheers,
Gianluca