Is it possible to make gift purchases of light novels and manga?
If you mean on the JNC site itself I believe the answer is currently no.
To the best of my knowledge, there currently is no mechanism at JNC's end of things for funneling monies to them on behalf of a third party.
If ya wanna give someone a gift of a JNC Premium Edition eBook or a JNC membership, ya gotta give said person the funds directly, saying it's for this purpose, and trust that they choose to use the funds for that purpose.
Now that the coin system is going to replace credits, might there be a way to gift coins to another user?
I would like for there to be a way for me to give someone a drm-free light novel or manga.
I would also like to see the ability to send gifts on the site. Either via coins or products.
Coins that the person may choose to spend how they want. This just needs a good, privacy respecting UX to select the correct person and the amount to send. Username is probably the most suitable identifier. Email would be unsuitable.
A product (book, manga, comic, audiobook etc) that people may choose to accept or not. This makes for a more personal gift in my eyes, showing that some thought went into it by the sender. Ideally this could be combined with a wish-list feature, though building the UX and back-end code around that would likely be more complex. Something like how Steam does this would work though. The accept step would be necessary to avoid forcing products on people they do not want in their library, aka the Steam PC Games store problem with "Bad Rats" back in the day where people intentionally flooded their friends game library with bad games like "Bad Rats" before it was possible to decline a gift.
Either way of sending gifts could optionally include the ability to attach a short note/message, again like Steam. However it might be a good idea to limit these messages to a curated selection like "Happy Birthday" or "Merry Xmas" to avoid undesirable messages. How tightly to regulate that depends on the level of moderation such a system would require.
I look forward to seeing what possibilities the new coins system and other back-end rewrites may bring in the future, even if its a bit off in the future still.