ER and HA environment questions

I'd like to start a separate thread on this issue. Based on the feature request thread, there were some folks requesting better functionality of ER in an HA solution. I'd like some feedback on that. 1) Why is ER being used for HA instead of HDR? 2) What specific functionality is being requested on ER? I realize that quite a few folks prefer usage of ER over HDR because the secondary server can be more than a read-only server, a sub-set of the main server, or on a different platform. However, HDR will always be much easier to set up and ER does not support a synchronous mode of replication. But I would like to get a bit of feedback on this topic so I can better understand why ER is being used and what the perceived pain points are with HDR. Thanks M.P.