Despite being older, these kanji are still part of the official kanji list, so they are not obsolete - in fact, they are required learning for tests like Kanji Kentei.
As a Japanese student, these are characters I have learned (with Anki) and not being able to visualize them is an issue.
I'm also not knowledgeable enough about Unicode to determine which characters have been changed, so I can't upgrade Anki anymore.
Unfortunately I don't have a better solution to offer you than sticking with 2.0 at the moment - normalization solves a bunch of other problems that affect more users, but as far as I can see there is not a way to work around these variants being converted to their canonical representation.
For future people reading this discussion, here's some useful information:
Upon further inspection, all the kanji being deleted seem to belong to the JIS-3 (JIS第3水準) character set, thus all the 6355 kanji of the JIS-1 and JIS-2 set should be safe (for now).
Keep that in mind when studying Japanese and store your JIS-3 (and beyond) kanji somewhere UTF-8-friendly if using an older version of Anki is not a choice.
Notepad++ and LibreOffice are compatible, didn't test any others, but you can use the characters I originally submitted for testing yourself.
Please add a disclaimer making people aware of the tradeoffs - users may find they can't search for non-Latin text added on one platform that uses a different encoding to the platform they are currently on.
What do you think about this? Bravo! Works like charm, I can open 2.1 with renewed confidence that it won't cause a mess.
I doubt anyone would suffer from tags or deck names being limited, but if filenames get normalized, that'd cause missing media, no? Unless Anki alters the filename saved on your HDD as well, not just the card field.
Please add a disclaimer making people aware of the tradeoffs The same should have been done for Anki 2.1.
It normalizes at the time of recording. So it won't change the filename, but if you edit the note, it will change the file reference < img src="XXXXX">. XXX is changed without this addon. So any notes that you added before Anki 2.0.32? or 42? will result in blank images.
Anki 2.0.52 normalizes media filenames, so any notes created by 2.0.52 will not be affected. This isn't in the changelogs, so I am not sure the exact version, but I am still using an old version 2.0.6 that is subjected to this error. So upgrading to 2.1 requires this addon to ensure data integrity if you have old notes made from old Anki version.