The current World Builder is only compatible with the default version of Boundless.
The new World Builder will only be compatible with the C++ version of Boundless.
(As you're both assuming - but I wanted to confirm it.)
Whilst the new World Builder is a big change (biome parts, the way part biomes are selected, new block types, new instancing / custom node / library system, updated GUI, map support) all the general biome + noise ideas remain the same. So it's definitely worth playing with the current World Builder, as everything you learn will be valuable with the new World Builder.