Ok, so one of the paramount useful features of Sketch is layout grids. Being able to define a layout grid with columns and gutters without resorting to a mess with guides is great.
I believe the Affinity could improve greatly on the Sketch grid, so here is my proposition for the improved layout grid and thoughts on how it could interact with the constraints feature that really needs to be fleshed out as well.
First of all
Affinity Layout Grid
Create Movable grids with columns and gutters
Grids should be resizable but should keep their ratios
Support for breakpoints in grid definition, eg. the same grid should switch to mobile view if resized smaller.
Padding around the grid should be separated from gutter values.
Support nameable size ranges (breakpoints) (eg. define XL as a range, L as a range etc.)
Affinity Improved Constraints
Support fixed distance padding eg. 20px manually entered
Constrain to columns from the layout grid
Support and remember breakpoints when constraining to layout grid
Toggle visibility based on layout grid range
Reflow text options
Support minimum flex, (eg. resize with this untill this unit is 100px wide)
support Div flowing, when resized smaller than minimum flex, reflow other objects as divs would.
Support different symbols based on layout grid range, toggle to replace an area with another symbol when going down to small views
I'd love to see any number of these features implemented, with things like this we could actually create responsive flexible layouts that would be able to be resized instead of creating multiple views for each page.