Seems CMorph is for you ?

https://moi3d.com/forum/index.php?webtag=MOI&msg=6373.1

And / Or Line web if you want some more curve on it!

https://moiscript.weebly.com/lineweb.html

Of course top can be planar closed if needing! :)

Here CMorph + LineWeb

Hi Matadem, you can find the cmorph plugin here:
http://moi3d.com/wiki/MaxScriptArchive

or for your curves case you may want to use Construct > Loft to build a solid between the shapes and then you can extract section lines from a solid or surface either by arraying a line and using Construct > Curve > Project or by arraying planes and using Construct > Curve > Intersect.

Here using Transform > Array > Dir on a line and then Construct > Curve > Project:







- Michael