FOSS communities probably won't form around most of these projects, as you said. Assuming the software can be managed by a few people with LLMs, likely local in the very near future, it's quite possible that plenty end users who didn't use FOSS before would jump on these instead of paying money to MS or Adobe. That in itself is a huge win for the majority. Depriving MS from revenue that is. Then for community FOSS, this has potentially significant positive implications about our biggest challenge - dealing with proprietary formats and proprietary blobs. This could mean perfect .doc/.docx compatibility in LibreOffice. It could mean a perfectly working nouveau driver for NVIDIA GPUs. How about fixing the tons of bugs we workaround in motherboard firmware. Or fixing that corner case in Wine so it can run your fav obscure game. Or reverse-engineering communication protocol of cloud-connected IoT to integrate it in Home Assistant. Etc. Etc.

In short: FOSS is a social activity. Assuming this method can produce very good source from binaries, that itself won't create FOSS communities, but FOSS communities can use it to significantly improve the FOSS they care about.