Hypothetical: Jungle respawn rate is increased to support one Jungler in each quadrant

Support becomes optional. Marksmen becomes optional. Do you keep a duo bot, or take advantage of five solo-lane gold/XP incomes? Three solo lanes would in turn allow a wider range of non-Marksmen to cover the bottom lane role. Because a duo lane isn't required, keeping a gimpy bottom tower probably wouldn't be wise. Adding a greater benefit to Harold would probably still be a good idea (permanent team-wide buff just like dragon, okay?) to encourage spreading power around the map. Removing the bonus XP that duo lanes gain to prevent solo vs duo from being completely out of control may be required.

Would game health improve?

Arguably, team comps would get a bit more interesting. Jungle items would probably need to be tweaked to encourage a wider range of viable Junglers.