I will be unable to update the old clients, so the bdb limits may be problematic. Refresh my memory again as to how Bitcoin solved it when the blockchain forked back in 2013?
they provided a patch for old clients to apply which limited the number of transactions to <= 4,500. anyone running the old client will need to have this patch if they don't want to fork. better if they upgrade to the new one of course so maybe just advise on site that old clients will be unsupported.