Well, I confess I am not an expert in ACM tools, and so I will not opine on it. Rather then, I'm going to focus on organization and management aspects, which for me is where the problems really exist, independently if we talk about ACM, BPM, or others. So, even tools support well ad-hoc or dynamic processes, with very friendly UI, easy to use,..., it seems to me that most challenges can be:
1 - How to ensure that opening this door, do not lead to loses totally the process standardization?. We all know that each thinks that his work is always special compared to the other;
2 - Without standardization, how to avoid duplication of tasks between the various processes?. This means wasteful redundancies, over-cost and low quality;
3 - Without standardization, how to identify performance improvements in each process?. Without patterns of behavior nothing is conclusive, making it virtually impossible to assess benefits from improvements.
4 - How to ensure standardization in key processes of the organization, and use the ah-hoc processes only in occasional situations?
5 - How to treat the information originated by had-hoc processes so as to integrate it timely into standard processes, as a governance process cycle?