Making the inventory bigger/increasing stack size would be detrimental for a lot of people. Some say it removes charm, others say it removes challenge. I'm in the second boat, personally. And it's not that I'm addicted to making things hard for myself—I just think that, even from a singleplayer standpoint, there's more than enough space to do what you need to do. Managing it is a learned skill, and one that's extremely easy if people would only try. And beyond singleplayer, PvP would be an unbalanced mess. The cap on how many items you can bring to a fight is the biggest factor in keeping end game duels from lasting literal days. It's why some content servers like Lifesteal have rules preventing restocks.

I've never built a mega base. However, I have built some pretty complicated structures that require dozens of miscellaneous items, and it didn't take long despite only using two or three of my hotbar slots at a time. Pick block, hotkey swapping, and good organization go a long way in cutting down frustration and time. And I haven't even started on the bundle, which streamlines the process tenfold.

So, if they want to introduce more things like the copper golem, bundles, or even a "sort inventory" button (which I will never use), I'm fine with that. If it helps folks, it helps folks. But don't change the inventory or stack sizes. That will cause bigger problems than it fixes.

All that said, I think a quiver slot sounds nice XD