I could work on one if the forum had a public API to make my job easier. That won't be viable until the new forum software gets released, and even then, we don't know if they will actually have a one.
I don't think that you'd (ever) want to do that.
Just imagine that somebody gets his account "hacked" (doesn't matter how), loses some Bitcoin and blames it all on you.
You may have even to make the code open source and it may still not matter for some (see Electrum scandal)
So I'd keep it official, with or without an API.
First of all, 3rd party apps shouldn't be trusted, it can be made for fun but not used for serious cases.
The author can also state that app is made for fun and he isn't responsible for any damage caused by this app (related to bitcointalk).
Btw even if the account is hacked and bitcoins are somehow stolen, it has nothing to do with an app. It can happen via social engineering or the user mentioned his keys in PMs.
Btw, for me, bitcointalk's app UI/UX will be a lot of fun and good experience.