The former already has boards to discuss and review inks, fountain pens, and paper. However, I don't think there has been any discussion on cute Diddl or other pictured / patterned letter writing paper / pads. I find the Diddl paper quite fountain pen friendly.
What about other places? There are groups on Facebook. Have you ever tried finding old threads, or topics you are interested in on a Facebook group? What if you take a break, even if it is only a week or so, it is difficult to see what you've missed.
What about the forum over at Interpals? Well, I have never found a long-lasting reliable penfriend there. Instead, I've had people with explicit profile pictures post messages to my profile, some marriage proposals, and comments/messages from people who have not actually read properly my profile. As for the forum, there doesn't seem to actually be a specific section for discussing letters and associated topics.
Surely there must be other places? Well, yes. One I did join last year but have had no success with is aimed mainly for females only (judging by the site's name), and although there are boards for specific age groups, the one for the oldies starts at 30!
I haven't looked at the number of female and male correspondents I have...
Another correspondence project has a forum but outside the time of the project, the site is not maintained and administered. I've just been over to check what has been happening and there have been lots of spam accounts opened, yet again. Letters are for life, not just for February.
So, where does that leave us? I don't know. Is there appetite for a forum with sections where you can discuss correspondence matter, maybe find new people to write to, et cetera? Maybe I should start my own?