I’d be happy if Blizzard gave us an extra Stash Tab that was a Personal Stash Tab. At least then we’d have a place to store extra items for multiple builds exclusive to our current in-game Character.
Even in D3 we get a maximum of 3 Pages with 5 Tabs on 2 Pages and 3 Tabs on the third Page. Although, none of them are Personal Tabs.
D3 gives us a maximum of 910 Stash Slots (70 x 13): https://i.imgur.com/wDFCXl6.png
D4 gives us a maximum of 350 Stash Slots (50 x 7): https://i.imgur.com/nDebG31.jpg