The her0ism angle is interesting,
Coincidentally, I recently just found out about him maybe a week or two ago on IG and read a couple of his interviews with Japanese outlets.
He's working with US and other artists and he has a more international outlook to his songwriting and producing vision. He is also interested in bridging Japanese artists into possible crossover success in the West. That's where Keiko traveling and potentially meeting with him may not be a case of her going on holiday or just tagging along.
It's exploratory and maybe even a little collaborative...maybe. I believe it's an introduction towards possible future work, and as an aside it would be a rare opportunity to run into US-based artists and industry people.
Relatedly, a fascinating thing to me is the massive international chart success that some Japan-based producers and artists have been having recently with homegrown JPop releases (anisong or Vocaloid-inspired), without necessarily (to my knowledge) working with foreign producers to tailor the sound to the international market.
That gives hope for the top and most well-positioned Japanese acts /producers to really break through to the world with just their own creativity. Babymetal broke a lot of barriers in the last decade for performing in the Japanese language and getting commercial and critical success including live touring in the West, with a fully Japan-originating team.