I think when all is said and done and we look back at the current run of Godzilla movies, its defining aspects will be mainstream acknowledgment and modernization and that absolutely stems from the fact that there are two concurrent series bouncing off of each other, not just in terms of production schedules, but stylistically. Shin Godzilla looks more visually similar to G2014 than it does any of the millennium movies, while having a style all its own. Meanwhile, Legendary has the benefit of Toho keeping the brand fresh and vibrant while they get their next movie together.
I think the Heisei era was kind of built around the idea that something like this might happen, with Toho making movies for local audiences while the specter of a Hollywood version that would play internationally loomed - but this scenario of two studios producing internationally-received flicks is a total pipe-dream. What a time to be alive.