If it helps, there are already at least two projects that do exactly that or something very similar: Despecialized and D+77/D+80/OTD83. The main project files are large, since they try to keep their encoding quality similar to an actual Blu-ray disc (~20GB+ seems about right for this). But there are also official AVCHD versions for burning to DVD9s, which are necessarily under 9GB, and even DVD5 downscales for those who don’t need HD. I also know that there are a ton of unofficial re-encodes of Despecialized that sacrifice a little visual quality for a lot of space savings, often putting the whole trilogy at under 10GB. If you’re looking for torrents, you’re actually more likely to run across one of these unofficial re-encodes than the official version, since there seems to be a similar bias in favor of small file sizes in that community.