As of today, we aren't planning any additional big DLCs after Land of Lions is out this Fall, no. We are still keen to do the City Life Cosmetic Pack, assuming that this month's Amusements Pack is popular with players (so feel free to help us make a good argument for it).
Anno 1800 has already received much more (and for much longer) post-launch support than any previous Anno game, and a certain point we need to set our eyes on the future of the team, and focus on our next project.
However, keep in mind that we had also not originally planned to do a Season 2 either, so things can always change. Game development is a very fast-paced environment to work in, that's for sure :)