I understand the limitations of the whole comparison table for vMix editions, they seems quite fair, but I cannot still get the point of limiting video sources input resolution.

I'll try to explain better:

Lets say I have the HD version for streaming purposes, or even SD, if vMix lets me capture video from my 1080p/4k camera, it will benefit from underscaling, improving overall image quality, while still streaming at a lower resolution, not to mention the benefits of cropping and zoooming the inbound video feed.

I know I can overcome this problem by capturing my own desktop (or other computer desktop lets say by NDI capture), but it's silly.

Please set the software limitations to output and canvas settings, even fullscreen preview windows if you wish, but not the input resolution, and you will contribute making this a better world :)

Regards.

Great to hear it! Last time I checked, it was not possible with free edition.

Any official confirmation of these limits?

Thanks

Also, to explain why it is this way, you answered your own question.
There is a benefit to scaling down higher resolution sources quality wise, so it makes sense to need to purchase a higher edition to use them!