What do you think about having a filter holder inside of the FTZ adapter?

Hi,

I own a Tamron 15-30mm f/2.8 G2 for Nikon and feel so bad that the Canon version has a filter holder in the back part of the lens! That is amazing and allows you to actually use a filter - and a very small and leight one, on such a wide angle.

I was thinking that the FTZ adapter could theoretically also have a filter holder in its own body, being just a piece of plastic with little electronic just to convert input/output. I wonder why didn't Nikon take this opportunity.

What do you think? Is my idea unfeasible? I am not much into technical stuff, maybe some of you could help me understanding why I can't have ND filters on my lens.

Cheers