#15 - May 10, 2016, 6:54 p.m.
The biggest reason to add a cost cap on Plea was the legendary that let you instantly have 20+ Atonements out at once. But that had too many other problematic interactions anyway; we're redesigning in a way that avoid them.
Without the issue of accidentally casting a 25-stack Plea, a cost is less imperative. It may ultimately be useful, but the flip is side that our general tuning desire for Disc is to bring the typical Atonement count down a bit, rather than facilitate it being higher. If there were a cap, it would likely be at something more like 10--allowing some room to get into inefficient territory where you almost certainly don't want to be going in normal play, with the cap only acting as a backstop beyond that. We don't want to undermine the Plea cost's effect of making it expensive to push your Atonement count beyond 6 or 7.
Power of the Darkside, in an upcoming build, should only affect a Penance if the buff was active when the channel started.