I'm not advocating the removal of Open Mode (or any change to the core system of Open Mode. I do would like to see some content additions). I play roughly 20% of my playtime in Open Mode.
That said:
Private PvE groups and Solo Mode is not enough or even close to what an Open PvE mode would be - in my opinion. Private Groups with players agreeing on not doing PvE is something different as an Open PvE mode that allows everybody to join, that doesn't depend on one player to admin the group.
And as an add-on:
If an Open PvE mode would exist - I don't think that FD will create such mode in the foreseeable future - I would still play around 20% of the time in Open Mode.
I'm not 100% against the idea of a dedicated PvE mode, as the mobius players and a fair amount of solo players would no doubt populate it pretty quick. Just concerned about the impact it would have on open, so I'm reticent to support.