Japan, Korea, Taiwan, Vietnam, India, Burma/Myanmar, Philippines.
Of those –
- Korea and Japan don't get along and their relationship is deteriorating.
- Myanmar – clearly aligned with China.
- Philippines- confused foreign policy and absolutely no defence capability whatsoever. Filipino army and air force are badly equipped COIN forces. Navy is mainly obsolete.
- India – will probably maintain own independent strategy ESPECIALLY as its main concern is still Pakistan. Note neither Japan nor USA nor Australia will want to rush to India's aid in case it has a another blow up with Pakistan.
- Taiwan – not recognised by most other countries on the planet. Given China's stance, letting Taiwan join is basically a liability and an automatic declaration of war.
- Vietnam – would probably be interested in such an alliance BUT close relations with Russia would probably hinder them joining.
Other players
- Malaysia – defence force in decline, closer ties with China
- Singapore – would probably be interested in such an alliance.
- Indonesia – would probably maintain their neutrality.
- Cambodia – close ties with China
- Laos – close ties with China
- Thaliand – closer ties with China.
-Australia – definitely interested in such an alliance.
– New Zealand – maybe.
A big issue is that most SE Asian countries have no military capability whatsoever.
For example looking at fighter aircraft in SE Asia (excluding COIN turboprops):
- Cambodia – 0.
- Philippines – 12 (T-50 armed advanced trainers).
- Laos – 8 Yak-130 armed advanced trainer.
- Malaysia – 39 – 8 F/A-18, 18 Su-30, 13 Hawk 200 (obsolete light subsonic jet)
- Indonesia – 86 – 33 F-16, 16 Su-27/30, 23 Hawk 200 (obsolete light subsonic jet), 14 T-50 (armed advanced trainer).
- Singapore – 100 F-15/16, 4 initial F-35 ordered.
- Thailand – 113 – 53 F-16, 11 JAS-39, 12 T-50 (armed advanced trainer), 30-ish F-5E/F Tiger, 19 Alpha Jet (obsolete armed trainer).
- Vietnam – 90-ish (48 obsolete Su-22, 40+ Su-27/30).
- Myanmar – 70 (30 MiG-29, 42 older Chinese F-7 (MiG-21) and A-5s (MiG-19 derivative). 6 Su-30 and 16 Chinese JF-17 on order,
It's the same with everything else be it tanks or air defence or frigates or submarines or transport capabilities.
Most of them don't even standardise calibres or communications equipment and most lack maintenance capabilities. This means virtually no inter-operability.
The only country in SE Asia with any serious capability is Singapore.
This means most of these countries are defence liabilities.