This would require additional multi CD containers to address, duplicating existing unique subtitles entries. Then, all variations would need to be individually addressed, based on media source, various FPS, release, etc. Lots of redundancy.
You do currently have the ability to download complete seasons of a series. However, this will download .zip of all episodes contained within that particular season. This will include ALL episodes, not just specific releases or format, and will require sorting.
You can also utilize the advanced, or very advanced search features to help identify the subtitles that you require, based on parameters of your choosing. This is helpful in selecting appropriate subtitles based on specific known good quantities.
Remember, limitations on quantity of downloads can also exceed the maximum number allowed per user/day, which would apply to many of the anime. I believe the number is 30/24. VIP members are set at much higher limits.
https://www.opensubtitles.org/en/support#vip