User blog comment:Deshiba/Mana Items./@comment-2248060-20140922115526

The issue with a flat mana item that gives MR is that it would ruin mid lane unless it was the same power or weaker than Chalice of Harmony or (just like Chalice used to before Athene's) it didn't build into anything so it was pretty much dead gold

Also it would be a Direct buff to Ryze's early game in mid lane and against magic damage tops (Maokai Alistar Mundo Nidalee, AKA the most popular top laners) and at the moment Ryze is in a perfectly balanced state.