I think at this point we would probably not remove the scripted metric aggregation without a deprecation period and a suitable replacement for the types of analytics users are using it for. The experimental tag still exists because up to this point we have not been completely happy with its API and this is something we are working to solve with changes like https://github.com/elastic/elasticsearch/pull/30111.
I think there is likely to always be a place for writing custom aggregation logic using a script (at least while creating a plugin that adds a new aggregation is still complex) but I would always see it as a last resort. Many times I have seen users reach for the scripted_metric aggregation before fully exploring whether their use case can be solved in a different way with the current aggregations. I am not saying that your case is one of these but I would advise exploring options for not using the scripted_metric aggregation where you can.
Also, as we are always looking to expand the list of out of the box aggregations, if your use case feels like it might be generally useful then feel free to open an issue on the Elasticsearch Github repo and we can explore whether we should build a dedicated aggregation to solve use cases like yours.