People often talk about how ports of old Touhou games are unlikely because ZUN lost the source code.
Often times people dont even know where the statement is from, another half of the fandom thinks the information is just made up.
But its still true that he did indeed lose the Source Code to these.
Theres a recent japanese news article that talks about this topic again (due to a Nikenme Radio broadcast i think),
and why its unlikely we will see most of the old games on Steam.
https://automaton-media.com/articles/newsjp/20200529-125704/
The translation for this article is as follows (there may be a few errors, but I hope you'll be able to understand the article)
The creation of ZUN's Touhou Embodiment of the Scarlet Devil (EoSD)'s steam release seems difficult due to the lack of the source code. ZUN, the main personality for the Web talk show "Starting from the second shop radio" episode 117th’s broadcast, the above content was discussed.
Before we get to the main topic, let's review "Touhou Embodiment of the Scarlet Devil". EoSD is the sixth installment of Tohou Project, a danmaku STG for Windows that was distributed at Comic Market 62 in 2002. Set in a fantasy world shrouded in red mist, Reimu Hakurei and Marisa Kirisame ride into a Western-style building in order to resolve the incident. It features familiar character such ass the vampire Remilia Scarlett and Sakuya Izayoi. It It's one of five Touhou Project Windows titles that are not currently available on Steam, with the exception of Touhou Mountain of Faith, Touhou Subterranean Animism, and Touhou Undefined Fantastic Object, which will be released on June 6. Though it is an older title, a Google search for EoSD shows that there are many new fans looking for a way to get it, with related keywords such as Steam, smartphone, PS4, and release date being the most common searches.
One of the problems with EoSD is that other Windows versions of Touhou Project doesn't run properly on Windows 10. Specifically, it runs super fast, with frame rates reaching four digits when launched in full screen. If played as it is, only a second will pass before the player would encountered Rumia with no lives. ZUN specifically had no idea what was going on. He tried to run it in window mode instead of full screen, but it failed to shift to the title screen, and the background music kept playing (this is in the author’s situation_ This is to be expected since it's a year after Windows XP was released, let alone Windows 10. But if a downloadable version on Steam was to be sold, these issues need to be addressed. If you want to play EoSD on Windows 10, please refer to the patches and various procedures that have been created by volunteers.
In the 117th episode of "Starting from the second shop radio" broadcasted on May 28, ZUN, the main personality, and Tetsuro Ogonogi, the editor of "Starting from the second shop radio", and other members close to him appeared using the meeting application ZOOM. As the talk progressed over drinks, Beat mario said "Please do something about EoSD:, and began talks about the missing Touhou titles that are not released on Steam.
Ru, one of the members on the show, said that "Perfect Cherry Blossom" and "Imperishable Night" would run on Windows 10 and could be released as it is if Steam;s test team would allow it, however EoSD would not run on Windows 10 and therefore could not be released. When he said that it would be quicker to remake the exe for EoSD, ZUN told us that he couldn't do that either because he didn't have the source code. It seems unlikely that EoSD will be released as is on Steam.
In the conversation about how to recreating the original, ZUN jokingly commented, "If I can't recreate something, I could just remake it and make money. I don't want to do a remake now because I think there's more demand for a new game rather than a remake," he said, which indicates how there might be an EoSD release someday. There was also the fact that it was a coincidence that all three titles were released on June 6th, and there was talk of putting Touhou Phantasmagoria of Flower View (which has a competitive mode), on Steam to support multiplayer. However ZUN said it seemed technically challenging. It should be noted that although the above was broadcast, it was a conversation in which alcohol was being consumed.
Though the broadcast was on youtube, the stream eventually progressed into gameplay of professional gamer Daigo Umehara clearing the Extra Stage of "Wily Beast and Weakest Creature" on Mildom. Remarks like “The more you get used to Touhou, the more you complain.” The event also featured live commentary from the developers. Since the broadcast also touched upon design and aim were also mentioned, those who are interested in this topic might want to watch Mr. Umehara’s broadcast as well.
Credits to
PurpleXCompleX
for the link, and myself for the translation.