Is the new Tcg pocket going to have a competitive option?, or would be used for strictly collecting?

Pocket will not replace Live, or have competitive battles, however, you can battle (it's just a little different from normal)

pocket was just announced, but presumably you can play other players if that's what you mean. We don't know if there's a ladder, or what the gameplay will actually be like as of yet. There is a breakdown on assumptions of what the gameplay features will be like that have been gleaned from the videos. Some key highlights of those features:
- 3 benched pokemon instead of 5.
- There are not prize cards, but points that you earn in a game instead. Ie an ex gives you 2 points, and a single prizer gives 1 point.
- Weakness isn't 2x, it's +20, and no resistances are shown on cards, so presumably no resistance in the game.
- There's an "Energy Zone" - nobody knows what it does for sure, but you don't attach energy to the pokemon like you do in the tcg.

It's not replacing live, as the normal competitive pokemon tcg gameplay is still going to be what is used at competitions, and people who play the TCG will likely prefer it over pocket. Pocket seems to be more of a "fast" game play, and it will pretty much be just a cash grab. I'm assuming they will have microtransactions so you can buy more cards, and all that stuff since live doesn't have any monetization options. Since they took away trading capabilities in live when they changed from PTCGO, it looks like you will be able to "trade" in pocket - who knows if that will even be something that is fun or worthwhile based on how bad PTCGL is.

Why not make a big update to the current one? Who knows, but it's probably because it's a broken company. Live has so many bugs, and they can't even do updates without taking down the whole game and server for users at least once a month. Literally one of the first things any development team should have accounted for is doing updates (without taking down servers and breaking the client, so it's seamless on patches). They literally could just add the features from the videos to TCG Live, and make a new "format" like Expanded vs Standard to house the new game rules. It is however a different company doing development on pocket vs live, so at least maybe it won't be crashing and hogging all your phone's resources while power draining your battery.