I thought that this topic would have found its way here already --
My first impression is that any angst one might have over United's policy would seem to be much ado about nothing.
Second impression is that on the surface it seems that United is merely codifying a uniform policy across its system rather than allowing what might have been local policies at one station that potentially conflicted with another station that could lead to customer service issues that otherwise were easily solvable before it blew up.
As I see it, the result is a more useful seating map feature, they say "dynamic" and a little more family friendly on the basic economy side of things. Now in addition to MileagePlus status members, families can now get free access to the preferred seats. Otherwise United does not charge for seat selection.
Just seems to me that United is making things a little easier all around and I don't think it'll impact my experience as a solo traveler.