Any idea on when a potential Xenoblade Chronicles X Definitive Edition and/or X Part 2 will happen?
i have no idea on port's they usually drop out of nowhere with no hint's.
Monolith new ip if it has a 4-5 year dev cycle will probably come out in 2022 or 2023, unless they started production after the hires in which case 2024 seems more likely.
sometime before then, that also depends on whether a XC3 is being developed, Monolith has been growing but it's worth noting on top of making new ip's, Xenoblade and port's of their old games they are also helping out with games like Zelda, Mario, Splatoon and Animal crossing, their dev team is spread really thin, XC2 was made by their side team and XCDE was originally supposed to be more of a upscaled port with change's only to the major stuff, for example the mechon were never supposed to get new models, they were given new model's as the dev team wanted to do that anyway. it's worth noting Nintendo also likes to complete games and then it on them for a few years, if something like that happens unless you have direct insider info it's hard to pinpoint when a game like that will come out.
we will likely see genealogy of the holy war remake this year, it's next in line to get remade unless they go after another FE game instead.
Tomadachi is mostly speculation on my part but that should be possibility as it's sale are gigantic in Japan,
Detective Pikachu 2 is also a thing for those who liked the first, Pokémon co talked about it during a press conference in 2019.
rhythm heaven has been disconfirmed as nothing was in development as of april 2020, however it's a profitable franchises so a game will eventually come to the switch.