so long as the last seen date relates to the last public post i don't see the problem
the relay should be blocking access to the DMs without auth from a party in the DM so they won't be counted
Discussion
The issue is not whether it is technically feasible, even in a privacy-conscious way.
I pointed out that no one seems to really care about that.
And this is in contrast to big services, where online status is strongly pushed, probably because this helps keep engagement high, with obvious economic goals.
well, i see no harm in putting it on a profile information display, but it isn't as important because you don't need it, the monetary incentive structure is different, it's not about advertising and influencing when users can do classifieds (already) and pay for their relays (i'm pretty sure some of them are now sustainable)