Converting Plan with Self-Directed Brokerage

Due to an acquisition, a small plan that has a self-directed brokerage account option for participants is merging into a larger plan that does not have self-direct. The purchasing company does not want to amend the larger plan to allow for self-directed brokerage. Would it be permissible to map the funds in the self-directed brokerage account into the age-appropriate target date funds, which are the plan's QDIA, upon conversion?

In order for a mapping to preserve protections under 404(c), the new investments must have reasonably similar characteristics, including risk and rate of return, to the old investments. If you think your target date fund will meet that standard, then go for it, but I think that's unlikely in most cases. If you can't map them to like funds then you will have to get a new investment election from the affected participants.