For reference, ZUN starts the Steam talk at 35:45 of
Nikenme #86.
Misc. things I gathered on a relisten:
(because I was first listening on a bus through shitty earbuds while asleep)- ZUN wants to release HSiFS-Steam before AoCF releases because he wants it to be first, while Unabara plans to release on Steam shortly after the AoCF physical release. This gives him a soft deadline.
- ZUN seems to further suggest that there wouldn't be any international features, if that wasn't already obvious.
- Part of why he wouldn't bring Touhou to Steam before was a translation requirement, but at some point that washed away so it's more feasible. Which makes it clear he doesn't intend for any sort of translation.
- He briefly mentions that he'd have preferred if Japan had a similar platform overtaking Steam, but since one didn't appear... [then Steam is fine]
- ZUN also doesn't discount the possibility of more of the games coming out, but I think everyone already assumed that without confirmation anyways.