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).
In fact, there are a dozen of penultimate Asian legs. The last three seasons had East Asia visits, Japan is totally overused that it was last visited in TAR 26. We should get an Oceania penultimate leg (probably Australia) the first time since TAR 11. Australia last visit was TAR 18 and hasn't visited since that should be taking a winter Australia leg.
Seasons without East Asia visit: TAR 3, 5, 7, 13, 22 and 25.
Overall of regional Asia visits
West Asia (Middle East): TAR 5, 9, 10, 15, 17, 23 and 28
South Asia (Indian subcontinent): TAR 1, 4, 5, 6, 7, 10, 12, 13, 14, 17, 18, 20, 21, 24 and 27
Central Asia (former Asian Soviet republics): TAR 13
North Asia (Siberia): TAR 14
Southeast Asia: TAR 1, 2, 3, 4, 5, 9, 10, 11, 13, 14, 15, 16, 19, 21, 22, 23, 24, 25, 26 and 28
East Asia: TAR 1, 2, 4, 6, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 26, 27 and 28