No, it is not going to be the last update. Mojang will continue to release updates for Java Minecraft. 1.13 will indeed more be a maintenance update, so I understand, to polish the game and to squash some persistent bugs. But it will not be the last one.
You mean the block textures to make them blurry
No, really, I think that I'll get a legacy resource pack. Or play modded
No, not really. Minecraft's textures are an embarrassing mismatch of textures that follow no rules and were clearly designed by multiple people who are not artists. Nostalgia cannot not cover up that fact.
This actually doesn't make sense. If the current artstyle is a mixture of different texture work in the first place, why would this matter? Mojang has constantly added new textures that didn't match the "old style". Did people specifically re-texture Jeb's work when it was clearly different from Notch's style? Not really.
More importantly, what exactly is the "old artstyle" when exactly 7 people have made textures, each with their own different style?
So you say that graphically, Minecraft is ugly? You're not better than people who say "MC is ugly because it's not having HD textures".
Re-doing the game's textures overdue to happen eventually. Because so many people have worked on this game, most if not all of which are not dedicated artists, a lot of the game's textures are inconsistent with each other and appear to follow no rules or art style other than being pixelated. The game started out with a dude screwing around making a game, then once the game actually became a game, Jeb joined and added his own stuff, who's artstyle is different from Notch's. Then Dinnerbone, TheMogMiner, and many other people made textures for the stuff they added which are all different from each other, and as of now the game is a jumbled mess of textures that follow no rules and don't go with each other.
Now it looks like they finally have a developer whose job is literally to make pixel art to crack down on the textures and get a consistent artstyle finally. Ultimately, we're probably going to see a lot if not most of the textures in the game altered in some way or redone completely.
One thing to keep in mind is that people aren't going to like these texture changes merely for the fact they're different. Whether or not the pixel art is better or worse is irrelvent, because all it takes for someone to complain about it is for it to merely be different. Old birch texture is objectively crap in context of proper pixel art and looks like someone stapled wallpaper with a Zebra pattern to a tree, but people have been looking at this texture for years and are attached to it. That can't be prevented and is simply something people will have to get over either by accepting change or using a resource pack.
They aren't fitting because they've only retextured a number of blocks. Once every texture in the game is changed, everything will match for once.
Together all of Minecraft's textures makes an artstyle that makes the game unique. If you change the textures, you kinda lose this feeling.