This interview with Mark Hamill about filming his rescue of Grogu is a fun watch. Hamill is always a treat, and the story is darling.
The idea, however, that this was a surprise is pretty suspect. With all the news and run-up to the finale, this was either going to be Luke or some other Jedi we expected to be dead. This was an 'if it isn't Luke it will be…' situation and when it wasn't someone we'd never heard of, that was the only surprise.
Seriously, to get a surprise out of me they'd have needed to bust loose Syfo Dias, Pong Krell, or Tarre Vizsla.