I enabled "World: Enable new enemies"
I tried different random and variation values. And multiple Factions are selected.

But still I only get one faction. I made a test creative map and fly around to find a few bases.

Bonus Bug:
Also I turned off the Nest and Worms scaling, but the new faction enemies are still scaled.

Factions tend to be less varied at the start of the game.
As you move out from the map center more factions will appear and as the game is played factions will mutate.

Do you have a save for the either of these bugs?

Ah ok I artificially increased the pollution and went more far away, than I saw different factions. So over time the factions gonna change too?

Also for the Bug with small spawners. It happen in every map with custom factions. I have turned "Attack Waves: Shrink Nests & Worms" off. No other mod installed. I would like to have them default size. Where and how should I sent you a save file?

Hi Spook2U,
the "Attack Waves: Shrink Nests & Worms" setting only shrinks the collision box of worms and nests to enable biters to move freely through cluttered bases and does not affect the actual size of nests or worms. the setting works for vanilla and new enemies.
here is the setting info text on mouse over:
"Reduce the collision box size of nests and worms by 50%. May cause overlapping entities due to the collision box being smaller than the entity graphic."

there is no setting for the actual nest and worm size for the new enemies.
the new enemies start out small but will get bigger as the evolution lvl increases.
If you want them to start out bigger you can increase the "World: Beginning enemy level" but this will also increase their health and damage

Oh ok I thought so because when I did enable the option default bases were small, when I disable default bases where big.

So do I get it correct, that the faction enemy bases also get bigger overtime??

Yes, enemy bases grow in both area they cover and the visual size of the spawners over time.