The European Mathematical Society Newsletter September 2018 issue includes an article by Mark C. Wilson (MathOA) and most of the editors involved in the switch from JACo to AlCo. Some key quotes:
In terms of community support, almost everyone has been behind us – support has been particularly strong among younger mathematicians.
Another of our initial concerns (as far as I remember) was the amount of our time and effort we would have to put into the flip. As it turned out, this was not so bad (mainly thanks to MathOA support) so other editors considering flipping in the future should not be discouraged by this matter.