I do know that there is some Manjaro 18.1 Previews around, but I would like to know if it is planned, or if it is possible to do a new release of the ISO images soon?
Manjaro 18.0.4 ISO images for official (flagship) editions were released in March 2019, so like almost three months. They start to be really old, and doing the initial upgrade starts to be problematic for some users. For example this case:
The only deal-breaker I know of so far for a mere maintenance release would be Calamares 3.2.8, because it sucks quite badly these days. Upstream released Calamares 3.2.9 recently thought, it might help to fix, or at least mitigate the situation.