These kinds of wealth transfers have been studied, and you do not need dark pools for them, just predictable trading patterns. See, e.g., https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5080459 on index funds or https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5122748 on funds that maintain a certain ratio of stocks to bonds (e.g., target-date funds). These costs can be larger than the actual management fees of the funds.