It's taken me less than 6 months to exhaust the exotics from Xur (through purchase and drops). Conversely my catalyst drops of late have been very infrequent. I'd happily sling the Nine some shards for the chance of a (non quest specific) catalyst. I know this would take a fair bit of work because once unlocked they don't drop again AFAIK, but it would be a nice way to keep babythulu relevant and keep the shard economy moving. I can't see that game play would be broken as a result.
Yea maybe like 500 shards a pop wouldn't be that bad. But leave raid catalysts in their respective raids for sure.