Thanks @moonsettler ! So far that’s the only argument I’ve actually heard for ECDSA, and it does only apply to legacy scripts (as such entrenched systems would need to be upgraded for any signing operation on Tapscript). So this would be an argument for ECDSA in legacy/witnessv0 only.
Keeping my ears out for any other reasons we may be missing for ECDSA in new sigops, but not expecting much 
So, the strongest form of this argument would be that there may be existing custody operations that have a ECDSA TSS implementation they trust and want to take advantage of some protocol like a post-signed vaults or delegation that use CSFSV. They have the resources to implement the new protocol, but not to audit FROST (or MuSig2 depending on their specifics) and move to Tapscript for that application.
I think this remains weak. Leaning toward making CSFS(V) BIP340 Schnorr only (but upgradeable with non-32-byte keys at a later time if I’m wrong).