Fathom has more renderings up on their website:
https://www.instagram.com/p/CkOvCLyPGGM
There aren't a lot of details about the building but I like how it adds some outdoor public space and some interest around the fringes of the Citadel (without a roadway cutting this development off from the hill itself). I think the space around the Citadel is underused and the quality of the roads and barriers around it is kind of low. It reminds me of generic park infrastructure in a rural area, but it is in the middle of a city. It is not terrible but it could be better.
If there were some kind of glassy modernist museum on the Garrison Grounds, built into the hill, as an example, I think that would be a big upgrade, but I wonder if such a project would be allowed. Bell Rd could also be realigned to make the land around there more useful (it seems Ahern is a kind of alleyway or parking area). Citadel High seems like poor land use and neither old high school has been redeveloped yet...