Necessarily, 1.13 won't be a "big" update. It might even be the last update. Microsoft said they would abandon PC Minecraft, and go onto Console and PE. So who knows happens after 1.13?
Source? This goes against everything both Microsoft and Mojang have been saying about the feature of Minecraft Java. Jeb specifically said they will not be dropping support for Minecraft Java, and that the game will receive just as much attention as it has always had.
In my opinion, the acacia logs look like they should be rocks, the emerald blocks remind me too much of Super Mario Bros. 3, the cobblestone is just "NO, YOU'RE NOT CHANGING COBBLESTONE, IT'S THE OLDEST BLOCK IN THE GAME," the cauldron looks great, the dandelions look a little weird, the bricks are fine, the obsidian is hideous, the diamonds are okay, I guess, the jungle doors look un-Minecraft, the crafting tables look great, most of the logs look great, the planks look awkward, and the iron blocks look absolutely astounding. The iron blocks underwent only such a slight change yet they look SO much better than before!
By the way, why should they fix stuff that doesn't annoy players? The main rule in development is: do not fix stuff unless it causes a problem.
Because the devs themselves consider it a problem? Jeb was pretty clear about why they're doing this, he doesn't like how older blcok and newer blocks clash because of the change in artstyle and attention to detail.