for those multichunk bases on multiplayer servers which don't load enough chunks to make it a bit faster to save big areas, maybe just a option to quick save with just adding Y co-ordinate

What exactly is the end goal of this...?

To make the saving of large areas a bit easier and faster

If you want to save a large area just use WorldDownloader. It's a much better tool for that.

From what i read it doesn't work on modded server like ftb infinity evolved

(I'm the maintainer of world downloader)

Newer versions (4.x series) should support modded servers to some level, in that it attempts to save the block mapping and handle custom dimensions. However, this isn't heavily tested. One thing that I can guarantee does not work is modded containers - the mod doesn't know how to convert the inventory slots into the block entity data. (But schematica doesn't handle that either if I recall correctly).

is this for 1.7.10+ versions or 1.10+?

The 4.x series only supports 1.10+. 1.7.10 doesn't have any of the compatibility changes - you still may have success with it, but it's luck-based since the block map configuration isn't saved.

One thing that I can guarantee does not work is modded containers - the mod doesn't know how to convert the inventory slots into the block entity data. (But schematica doesn't handle that either if I recall correctly).

Correct. None of the contents are saved at all, unless it's saved in SP or with the command.