Here's my newest theory:
I can see Mitsu doing a rebadged Nissan/Renault for Europe and possibly North America, where the Mirage was met with the harshest criticism. Possibly call it the Colt and drop the Mirage name.
The problem is the very important ASEAN market: the Mirage was a huge success there (200k before the first 2 years), and was intentionally designed to straddle the A/B segment, unlike the Clio/Micra. They won't want to upsize to a B for those markets. The Clio/Micra variant may be too expensive, and also there's no sedan version, which is important (see Philippines).
I bet ASEAN countries continue to get the Mirage based on an evolution of the current platform. I suspect design work on the next gen Mirage was well under way before the Nissan merger.
I actually dreamed up this theory and THEN stumbled on this article saying many of the same things...
(from November 2017)
Source: https://www.just-auto.com/analysis/a..._id179448.aspx...the next Mirage, which is due in 2019. The architecture should be an update of the current car's, which is called 'MMC Global Small'.
[...]
The next Attrage / [Mirage G4 sedan] should be on sale from mid-2019.
At the moment, MMC has no B segment/Subcompact car. This situation should be remedied in 2020 or 2021, when a new model based upon the next generation Renault Clio is added. It will likely be built in Thailand and/or Europe.