>>41191991KFP here. Kiara said back in October that they were going to have a full Myth meeting in Japan, but no date had been set yet, so she wanted to go on her own before then (I didn't expect Ame to do the same). Kiara later said that if she had known that the second trip would be so soon, she wouldn't have spent the money for her own.
She also mentioned that she wanted to attend the WonFes convention that will be held on February 12. So it can be considered a possible date for their return (but it's not certain).
And she also said that she'll surely have a good streaming environment next time, it's already been decided. So we can expect Cover to rent a separate house for them, like they did for Council.