judgeing by that picture....

It's just Pikachu and you can give your Pokemon nicknames so I don't understand why they care so much.

Nope I'll still call them Dolphins.

Why is this just happening now??

This is the problem. While this is true in Cantonese, it's actually the opposite in Mandarin. What they are doing is basically changing the spelling to what Mandarin Chinese speaking population has been calling Pikachu. The reasoning behind the name change would probably be so that they would not need a specialized translations for Cantonese considering Cantonese speakers can still read Mandarin, despite a different pronunciation. Their concerns are understandable though. Imagine getting a name changed into one that would be pronunced correctly in Spanish but different in English.

I think it has to do with the underlying issue of Chinese control on aspects of Hong Kong that were originally free for the locals to decide on.

I think it is one or the other. They had to choose between having the same pronunciation or having the same characters. They initually chose to have the same pronunciation. Now they changed it to have the same characters.

Chinese control? Hong Kong was originally part of China for centuries until the british robbed it from China for refusing to take and buy british heroin. 

It's like Disney renaming Mickey Mouse "Michael Mouse." What else kind of response did they expect?

I am so tired of explaining this BS...

Nintendo HK already released a statement to the petition group asking for another set of Pokemon translations, citing that the new name for Pikachu in Cantonese can, and should be pronounce as Pikachu, not "Pei-kaa-jau". Nintendo never intended to restrict the name's pronunciation. People should really stop bringing goddamn conspiracy theories and politics into this. Do I need to remind you that Nintendo is a Japanese company?

On top of that, these people that protested are not people that will actually buy the game - they are just political activist that tries to link this with their agenda: search up Civic Passion. At least use a Chinese company next time, geniuses.

It disgusts me to see media outlets making this out to be a huge thing - it's not. A local 3DS meet-up in China can easily have 30-40 people, and the Pokemon Chinese Localization Campaign organized by China Mainlanders two years ago have around 25,000 people in the end. Why don't I see the likes of CNET reporting on that? Fucking click-whores trying to stir up controversy.

And it's not like the Pokemon names are not compromise for the mandarin speaking areas - a lot of other Pokemon receive name change that differs from their Mainland unofficial translations/Taiwan official translations.

Some examples:
3D龙→多边兽
比雕→大比鸟
素利普→催眠貘
素利帕→引梦貘人
艾比郎→快拳郎
乘龙→拉普拉斯

TL;DR:

The situation now for name Pikachu in Chinese is
Mandarin: Same name, same pronunciation
Cantonese: Different name, same pronunciation

PS: Pikachu is in its root, a foreign word - nothing wrong with using a different pronunciation than the characters itself.

PS2: And no - the HKers does not have to relearn all 700+ Pokemon names, because the names were unify starting from Gen 3.

PS3: Right now, the first ever Pokemon National Championship hosted in HK is in danger of being cancel because of Nintendo's fear of these people due to their track record and with the precedent of the Boston incident. Someone in HK is 1 fucking point away from qualify in the PWC, and now he has to go to Singapore because of these good-for-nothing SOBs.