Inviting Japan into this dispute is like applying a damage buff to PLA, it doesn't make PLA intimidated it makes them more likely to throwdown since it's now two birds with one stone.
Also as others pointed out, Japan can't even control Diaoyu Islands, what hope do they have in the much further SCS?
Let says Japan were to interfere and take side in the SCS, there is a likelihood that China will take the opportunity to reassert her control over Daiyu Island.US will be dilemma.
Filipino has forgotten about the Massacre of Manila back in 1945.
The independence of Ryuku will be reassured and will be fully supported by China at that stage.
The Ryuku already have a resident representative inside China.
Where will US relocated their Airbase in Kadena to, if Ryuka backed by China ordered their eviction then?
Philippines? Chances are slim.
Deterte will be back in power by then.
Bongbong is just a one term President and a shortighted one.
Can't blame him as his family has always got a history of corruption and can be easily bought by the highest bidder.
The era of Deterte represented progress with no conflict but Bongbong, a period of stagnation.
Deterte recognized that these islands may means nothing to Philippines but for China it is of strategic importance.
The strategic islands curently controlled by China represents more of a threat to US than either Japan or Philippines as the objective is to detect every underwater vessels beneath there. The USN can no longer performed their first or second strike beneath the sea there.
Philippines, an ant will be trampled by the elephanta when they fight.
Interesting times.
For Philippines today, they lost the forest because of a tree. What can we say?
He was practically snubbed at ASEAN.