The popular comics wouldn't probably even want these boxes because they are already well known on Tapas so it wouldn't really benefit them due to having achieved market saturation. For example, would there be any point in Sarah's Scribbles running ads? A reader pretty much has to be living under a digital rock to not know about the series.
The boxes would most benefit those series on the app that have no featured footprint and have very little to no chance of ever being featured (gray scale, long form, right-to-left, non-BL, one page updates, etc.).
If anything it levels the playing field for the start-ups who are at the bottom of the pile and want to invest in themselves to try to move on up. Since popular comics produce the most views, they would benefit the most from the increased ad revenue.