And they could sell more slots... Bring the total to 10.
An extra row for making spells would easily fit. I think the improvements to faster crafting times were sweet with each MA improvement purchased. You could add 5 more levels and at the end of it have 1.5 hours per relic instead of 2.
And then for recipes, extra tabs there could be sold separately... Would be more challenging to fit those in, but I think more people would pay for an extra recipe than the 50 diamonds a pop to renew.
I thought they could also sell more spots for hours you can collect KP, to 15, then when you double down you have 30 hours, or 30 kp.