The Godzilla Monster Planet sequel has been announced, Godzilla: Decisive Battle Mobile Breeder City (?), and it appears Mechagodzilla will be apart of it. The sequel, which also has a poster revealed as well, is scheduled for a May release and a ticket pre-order has already started with special early pre-order bonus of a clear file with the movie poster image on it (below)as well as the image on the ticket too it appears. The reveal was accompanied by some info (translated from Japanese) -
"What does "city" that was left on the earth after 20 thousand years that all urban institutions should have been devastated? Also, in the Tizaru visual, there is a scene that cuts out the moment that Humanity confronted <something> in the darkness where rubble was stacked up.
Whether the "mystery" that springs up in the movie "GODZILLA Monster Planet", the novel "GODZILLA Monster Revelation" is revealed. "GODZILLA Monster Planet" In the prehistoric period, what is "What is Mecha Godzilla", a godzilla decisive weapon secretly developed by mankind?".
More info as we get it on the sequel.

Janus Films/Criterion have obtained the rights to nearly all the Showa era films (except King Kong Vs Godzilla, Godzilla Vs The Sea Monster, Godzilla Vs Hedorah, and Godzilla Vs Gigan) as well as Rodan and War Of The Garganuas (International Dubbed Version). The films have already hit the Starz cable network but could there be more to come. The place cards on Starz (which look like potential Blu-ray/DVD packaging) are all very similar with basic styling. So what does this all mean going forward. It is odd that they would go to Starz first rather than get a Blu-ray/DVD release first, Sony's Godzilla films were first released on video and since have shown up on multiple cable networks and services (Hulu, and Starz most recently). It is possible they are waiting on release of Legendary's Godzilla 2, and/or Godzilla Vs Kong to piggy back on their popularity, another possibility is waiting on Toho's 4K restorations to be completed (although that could be a while). Some rumors have suggested a box set which could be nice if it was the complete Showa era. The big question is will fans get these if they are released most fans more than likely have most of them and wouldn't probably get them unless there was some added bonus. Hopefully we will get more info soon on the potential releases. (Note: some info here is from various posts from Facebook and the web (like August Ragone and others).