Can you still purchase the microtransaction packs?

Yes, you can still spend real money. At least, it's an option on the 360. I haven't bothered to transition the game to Xbone, but I don't see why it would be different there. That being said, I wouldn't recommend it. You'd obviously be better off just spending in-game credits from matches. If you are dead set on wasting actual coin, I'd only suggest Reserves Packs for the higher character card chance. That is, of course, if you have a lot of characters yet to unlock.

But seriously, if you find the unlocking process slow going through normal means, just have some people here carry you to glory. Terminator Force, as I understand it, has very large muscles.

It's the same on the 360. For instance, if I go to buy an Arsenal Pack, I'll get two options: "99000 Credits" and "Or 240 Microsoft Points." If I select the "Or 240 Microsoft Points," then I can either buy it with a credit card/debit card/PayPal account set up to my profile or redeem a code off one of those gift cards you see in stores.

Although, again, I wouldn't recommend doing this.