Currently working on the Catalog Professional quest, and that means finding trades to rank up from bronze to silver.
There are a lot of trades, so my current method is to look at which outputs are silver, flagging them as favorites, then hiding favorites.

Adding a dropdown box or clickable toggles (like the planets) to filter trades would be helpful: Any, None (pre-bronze), Bronze, Silver, Gold, Red

EDIT: In the case of trades with mixed ranks (eg something that has two bronze and one silver) it would match as long as ANY output item matches the filter (so this trade would match "any", "bronze" or "silver").

EDIT2: Another idea: a filter for min/max productivity% with an input box. Eg, only show trades that have 35% minimum prod, or ones that are in the 5-25% range.

You can already sort by total trade productivity in ascending or descending order, which of course is strongly correlated to the item ranks in the trades. Expanding on your great idea and more seamlessly integrating it into the trade overview, I can add an option in the item selection GUI for the item slots where you can -- instead of a specific item -- select a wildcard item restricted to an item rank. Then it can be mixed and matched as much as you prefer, de-necessitating the "ANY" type of filter.

The trade overview already combines the various filters as an "AND", so in your example of one silver and two bronze items in a trade, you may do either of these things to include that trade in your filter using this new feature:
- Set an item to be a wildcard bronze item,
- set an item to be a wildcard silver item,
- set two items to be wildcards for bronze items,
- set a wildcard for bronze and another wildcard for silver,
- or set two wildcards for bronze and one wildcard for silver.

And you will find that the last method listed above (for example) will not yield trades with "either two bronze OR one silver" but instead only trades with "at least two bronze AND one silver".

Coins are an edge case. While they are items with a gray rank under the hood, they will not be considered items by this new filtering feature. That is, a wildcard item for a specified rank, even gray rank, will not let coins through unless another item is on the same side of the trade as the coins and happens to have that rank.

I like your idea and think this can be implemented in a way that avoids adding noise to the trade overview GUI while extending functionality along yet another axis. Thanks!

No problems! Like I said, it's perfectly useable as-is, but that's just a handy little QOL quirk that I think would go a long way.
And of course, as the mod author, you have the best idea of how to approach and implement it. (looking forward to eventually getting to another planet in my current run)