I read here that it supports ingestion from BigQuery and GCS, however, I was wondering if it supports simultaneous ingestions from various sources
At the moment, You can select datasources from BigQuery, Cloud Storage or to your local computer. You can see more details here: https://cloud.google.com/vertex-ai/docs/featurestore/source-data
In addition to @nceniza response, I see in your question you were asking about simultaneous ingestion. I'm not seeing anything that would indicate that we couldn't ingest source data from MULTIPLE sources simultaneously. I'm also seeing that you can ingest data through API streaming. So if your data isn't already available in BQ or CMS, you appear to be able to ingest through sourcing the data yourself in an app and streaming it in through API.