Is it possible to make a plane out of meta objects? Yes, I know, Add > Metaball > Plane.

But how can I make a large plane?

Scaling it affects all meta objects in the scene.
I thought of connecting a bunch of meta planes together, however this isn't a perfect solution as it's a little bumpy (and if you need a really big plane it won't help your framerate)  



How can I do this?
Plane meta-elements have an X and Y Size you can edit in the Properties editor > Object Data > Active Element:



it looks like this is what you are trying to achieve.