For IPFS, I'm fairly sure you can now serve from your normal filesystem, rather than load it into their blockstorage -- or at least the blockstorage has pointers to real data blocks that are part of your existing files (it's the nocopy option[1]; it's marked as experimental, so there may be some sharp edges.)

For Filecoin, if you want fast access, you do need to keep a second hot plaintext copy, as well as the sealed Filecoin copy. But that works for the backup case for IA, because the hot copy would be served from the archive's existing infrastructure (and/or a distributed IPFS hot cache) -- you'd just use Filecoin for the proven safe backup.

The project to back up IA to Filecoin is still ongoing. The IA dashboard that shows the current state is (perhaps predictably) down at the moment, but it crossed the 1PiB line last year[2], and they've been optimising the onboarding flow recently.

[1] https://docs.ipfs.tech/reference/kubo/cli/#ipfs-add

[2] https://blog.archive.org/2023/10/20/celebrating-1-petabyte-o...

(Disclosure: I work at the Filecoin Foundation/Filecoin Foundation for the Decentralized Web, which partners with the Archive on this project, as well as supporting other Internet Archive backup projects.)