Currently the side panel section is dead space clearly only there to house the advert window.
Why not have the space above it show something relevant such as a list of either popular addons or recently updated addons. Or it could show off a random addon (one that's compatible with your game version)
If a user pays to remove ads, they could still choose to have this panel there, but extend it the entire height of the window, or just hide it entirely. I think that would be better than just having ragnaros staring at you.