Original Story [Fri 18th Jun, 2021 21:00 BST]: 2021 may just be the year of the Metroidvania, and not for the reasons you think. The Nintendo E3 Direct earlier this week revealed the existence of the first 2D Metroid game in almost 20 years, Metroid Dread, and now (via RPG Site) we may have ourselves a re-release of the Game Boy Advance Castlevanias.
On the 18th June, 2021, Konami registered the title "Castlevania Advance Collection" with the Australian Classification Board, which, of course, means that it also appeared to the public (thanks, Australian government!). The author is given as "M2", a Japanese studio whose work includes the 3D Classics on Nintendo 3DS, the Castlevania Anniversary Collection, and the Contra Anniversary Collection on Switch.
It's relatively safe to assume that the Castlevania Advance Collection will include the three Game Boy Advance games that were left out of the Anniversary Collection: Circle of the Moon, Harmony of Dissonance, and Aria of Sorrow. It might include some other titles, too, but the "Advance" in the title is certainly leaning more towards the Game Boy era.
Castlevania Advance Collection looks like it's also destined for release on multiple platform, so it'll likely come to Switch as well as PC, Xbox and PS4.
Who knows when we'll get to hear more, though! Keep your ear to the ground, and make sure to treat your GBA nicely, or Konami might change their minds.