It's far from a perfect solution, but a friendly reminder that until they fix the issue (I don't see how it's so difficult to fix that 1.15 pre-releases are coming out with it) there is a work-around you can use to enjoy your game in the mean time.
Razer Synapse (if you have a Razer keyboard), iCUE (if you have a Corsair keyboard), Logitech SetPoint (for Logitech keyboards), SteelSeries Engine (for SteelSeries keyboards), KeyTweak, Map Keyboard, Sharp Keys, ATNSoft Key Remapper, and probably many more made by all kinds of third party people and gaming keyboard manufacturers all let you remap specific keys for as long as you have the program open/the profile set. You can download one of these and temporarily swap Tab and E while playing, and it'll go back to feeling like normal.
We shouldn't need additional software to enjoy games, but if we have to...
Edit: I am very sorry Ezekiel, I didn't see your post until after I'd hit submit since I was typing before you posted yours.
I'm pretty sure Ethan has a valid point. Tab doesn't actually do anything but alienate players that have been using Tab as an inventory button for years.
As of right now, Tab literally doesn't do anything but highlight the recipe book button to be blue. You can't open the recipe book with it, enter, or any other key on the keyboard - you still have to move the mouse up to it and click it. (Technically maybe having the button blue makes it easier to see if you can't see the color green?) But once you've clicked it open with the mouse, Tab still doesn't do anything. It doesn't allow you to move through different items on the page, or tabs in the list... the only thing it does is turn the button blue... ...and also block you from using Tab as the inventory button.
It's quite literally making the game less accessible for a decent group of people (check the watchers and voters here, and do a quick search on Google/Minecraft Forums/Reddit. A lot of people are complaining) but doesn't actually help anyone.
Also, what I find most hilarious is the upper management. "Right now we need to have a certain degree of accessibility in the game or we are not allowed to do any more updates." sounds like a suit who has no idea what the game actually needs, but wants to announce to shareholders that they're making improvements to the game. "One of the requirements is to be able to navigate in menus without using the mouse" but yet you can't actually navigate the game without using the mouse. You can't open the recipe book (which as someone who has been playing since 2011... you don't need it to play the game anyway) or navigate through it, or craft anything with it. Or move items around in your inventory, or move items from the inventory to the crafting grid... you can only turn a button blue with Tab. Oh, and can no longer use it as a normal button.
I feel bad for the devs, I really do. I know it's not entirely their fault (they could make fixing a bug they introduced a higher priority). But it still comes off as making the game less accessible in the name of greater accessibility.