IMO the worst part of the game is the sell tab of the shop. It's a huge chore to click through every items to search for trash every time the inventory is full if you want to keep your options open and want to keep several alternative items.

The filtering in the inventory screen is great. So from my point of view there are two solutions for the problem: Either add the option to mark items as trash from the inventory screen so that they can sold with a single click and/or add the category filters from the inventory screen to the shop.

I would prefer prefer a combination of both possibilities.

Are there any plans to improve that part of the game?

Look for this: you can sell all the trash with only one click at the shop...

This would be very useful. I think mk47at has meant by "trash" the items you don't need, not exactly scrap items.
Sometimes you find a weapon or add-on you don't need and you could mark it as trash and sell later without searching for it.

Another great (and expectable!) fature would be comparison of item stats to currently equipped.