Hi   what are your source types ? are they raw files or delta table ? I dont think extracting specific key from object is a heavy task, Also what type of transformations are you expecting on these metadata columns by consumer teams? usually metadata columns carried forward for maintaining lineage .

now talking about transformation if you are going to do mutli record to single record transformation then how will you manage row_hash_id for this single record? you have to make a list of source hash ids and then store in there which is already difficult

pls see attachment