In the Shape Tool - Line Shape -> lock ratio, this currently constrains the lines to be diagonal.
IMHO it'd be a more common use case that users would want to constrain a line to be horizontal or vertical.
I would suggest changing the default behaviour of the ratio lock for line shapes to be horizontal/vertical and not diagonal.
You could leave the Ctrl key modifier to still constrain diagonally, but add a Shift key modifier so that holding shift constrains the line vertically / horizontally (this would coincide with Photoshop behaviour).
I know it's not a great idea to change behaviour on published code, so could consider adding a LockRatioMode property to the shape tool that defaults to Diagonal, and allow coders to set it to HorizontalVertical to implement the new behaviour.