Lucario is one of my most favorite Pokemon of all times hahaha.
Lucario for A-Tier? Possibly. Quite Possibly.
I've had a lotta success with Lucario. The biggest problem I feel is if one doesn't play Lucario smartly (Like sending him out turn 4), Lucario will be a deadweight. Lucario requires Rocks quite a bit. He also needs certain threats eliminated, and sadly, the list is a bit on the extensive side. However, once Lucario gets +2, it is so hard to wall that beast. Not even Skarm can take a +2 CC after Rocks. Lucario has a great movepool that is hampered by 4MSS. Can he sweep the mast majority of the metagame? Sure. Only if it's late game. Lucario is no Terrakion, but he certaintly is a huge threat of its own kind. The reason I cast my vote 70% in for Lucario, despite these flaws, is because Breloom made it to A-Tier. Lucario, I feel, is able to perform on par with Breloom. With Higher base speed, a +2 Priority move (as opposed to Mach's +1), and a better movepool Lucario has a shot in A-Tier. Also Lucario has the SEXIEST typing in the world, that makes so many other sweepers drool in envy.