Named point in the transaction log? Does it exist? Is it possible to create a named point in the transaction history of the database, such that a subsequent connection could retrieve data at that named point in the log?

For example, lets say there is a loader process that is writing to multiple tables fairly often. At some point, a reader process creates a named point in the log, lets call it point A. The loader does some more updates and now we are at point B. Then another reader process comes along, and can select data as point of A.

Is such a thing possible in SQL server?

Unfortunately, the tables / loader doesn't have a bi-temporal structure, so the reader can't supply an as of datetime as a predicate on the select statements.
You can use a Log Mark to enable a restore to specific logical point-in-time of a database, but you can't use that in queries to the main database.

You can take a Database Snapshot to present a point-in-time consistent copy-on-write snapshot of an existing database.