In my understanding MVCC's primary use case is to use interactive transactions over iproto. I don't know about a cost of a really long living transaction, but (as far as I understand) MVCC is not designed for analytical queries. It is for OLAP workloads.

Tarantool Enterprise Edition offers user read views that has a C API that can be used from a separate thread. It is for analytics.

For Tarantool Community Edition I would suggest to join an anonymous replica to perform analytic queries. This way it doesn't affect the primary (OLTP) workload. However, it costs the memory.