It will not be possible to port maps from OMSI to LOTUS, they use a completely different and incompatible system that will hopefully be a lot better.
However, there is no release date for Rails of LOTUS let alone Streets of LOTUS... and I wouldn't be surprised if it's 2020 before it shows up, given they haven't started work on it yet and are still very busy working on the core of the graphics and such.
It's also not like everyone is going to jump ship immediately as it's released either; people will keep playing OMSI until LOTUS can give them they experience they want in a bus simulator. People still play maps and buses for OMSI that were made many years ago, even though much higher quality content exists - unless a newer version of that exact map or bus gets released, they'll settle for worse quality.
With that said, spending time working on a map for OMSI and never releasing or finishing it does not mean that that time is wasted. The knowledge of how to use the OMSI Editor may only be somewhat transferable to LOTUS, but knowledge of how to recreate realistic roads, model buildings and create realistic scenery absolutely will be.
For reference, here's a screenshot of the level of my mapping skills after just a year of owning OMSI, with no prior experience:
Like all of the maps I have started, this is little more than a couple of tiles, but just making something small and working on identifying where to improve it is enough to learn at least something. This wasn't the first map I made, and I wanted to make something good rather than just something, which is why it's better than several other maps that have actually been "finished" and released.