I would love to see filters for linked fields. The filter would function like a drop-down that would limit the items you can select in the linked field. I can think of quite a few applications for this.
MiniExtensions has this functionality and it is amazing! You can add any number of single-select, multi-select, or linked fields from the table you are linking from. https://miniextensions.com/filter-linked-records-in-miniextensions-form/
A few applications:
Time tracking: Your company tracks time by projects and sub-tasks of each project. You could add a linked field to sub-task, and filter the list by the project.
Order forms: You are generating quotes or invoices using Stacker, and adding line items. Your backing base has two tables: products and product configurations. For example, we sell the same chain hoist with different lengths of chain. Same product, different configuration. You really want to attach the "configuration" to the order form, but would like to filter the list by product or brand so you can find the SKU more quickly.
Addresses: You could filter states/provinces by country.