TAR29 most likely might host two Vietnam legs.
As for penultimate legs, Japan/South Korea/Taiwan (China & HK not counted as they visited on last two seasons) would be the highest possibilities as East Asia provide multiple flights back to US which is convenience for them. In fact South Korea and Taiwan last visit was 17 and 19 respectively which both deserved for another visit, and for Japan the TARUS have the pattern to visit there every 3 interval season and the last visit was 26 which fitted the pattern for another visit. lol
Penultimate legs in SEA was less possible because it would need to go west again (except Philippines, but then it get visited on 25.), and they would need to connect East Asia airport in order back to US. (See 25 as they connect Tokyo Narita airport back to LA).