Pep said all the keepers need to play and that second choice will rotate, he name dropped Gunn so I think we can assume he's considered a first team keeper now.
Personally I think if Gunn's going to have any chance of a future in goal for us, he needs to spend as much time around Bravo and Pep as possible, and if he is going to go on loan, it has to be to a club with a similar philosophy of playing out from the back - and that's a very small pool of potential clubs.
Loaning him out to some random League 1 or Championship club will be absolutely pointless, any benefit or growth in his shot stopping or traditional goalkeeping skills will be completely mitigated by the fact he won't be doing the training with ball at feet which he'll get here. I'd much rather he stayed as 3rd choice keeper, taking part in all the drills with outfield players, rondos etc, playing the way Pep wants his keepers to play every day, practising and learning off Bravo.
Realistically we all know Willy isn't up to much. At best he's marginally better with his passing than Joe was, and his contract is up in June. If Gunn has any real potential at this level than he could end up 2nd choice keeper next season, at 21 playing cup games under Guardiola.
If he goes off on a loan for a year, there's no chance Pep and co will be comfortable enough with him to step up to 2nd choice.