I finally watched the Kiryu Saga

My only issue with the Kiryu Saga was that it ended too abruptly on a cliffhanger that was never explored (something that's a reoccurring issue with the Millennium and Reiwa series). Other than that, Godzilla Against Mechagodzilla and Tokyo S.O.S are both really good.

Some things are left better unexplored

I only need to watch king kong vs. godzilla and godzilla 1984 and then I will have watched all godzilla movies.

well Toho could later come back in a later movie and finish that plot point

What was unexplained?

Well not explain but expand on the stinger if they so choose to make a stand alone movie like what the Kiryu saga did for Mothra and War of the Gargantuans. I wish I could have saw GxMG on the big screen but stuff happened.

The stinger was just there to ominously communicate that humanity didn't learn their lesson. What happened after doesn't really matter it's just an emblematic moment. The story itself is complete though--It was about that Godzilla and that iteration of MechaGodzilla and it was completely wrapped up by the end of Tokyo SOS.

I wouldn't be against a continuation of that continuity, but given how Tokyo SOS flopped...

Probably explains why they went for Godzilla Final Wars instead of continuing the Kiryu saga

I might go on another Godzilla marathon soon

Final Wars was being written by Wataru Mimura about 6-7 months before Tokyo SOS even hit theaters. (Which might explain why Mimura didn't come back to write Tokyo SOS.) No matter what, Shogo Tomiyama seemed pretty determined to go a different direction.