As I understand it, supporting EH-safe containers is a non-goal for most project contributors. There’s room for solutions that work for everyone in LLVM, and as long as making DenseMap more exception-safe doesn’t compromise code complexity, code size, or performance for other users, those improvements are welcome.
However, as mentioned, you would probably be the primary stakeholder of the EH-enabled configuration, and be the one setting up and maintaining build bots to cover it, or living without them.