Integrating bitcoin to my application

I'm writing a virtual world renderer (FOSS, GPLv3) where the users have the ability to send each other cryptocurrency of their choice, but I'm having problems with integrating bitcoin:

• Transactions take too long
• Impossible to mine on consumer hardware
• No privacy whatsoever
• Non-fungible
• No smart contracts

Are these things being worked on by the devs? I know there's Bitcoin Lighting but that seems to be a separate project.

I'm writing my own wallet in C++ while using the official wallet as a reference.

I've added support for a couple of other cryptocurrencies that lack some of these features but so far they've been at least more feature-rich than bitcoin.

Is there an L2 solution I could use that tries to solve some of these issues? Or should I create my own L2 layer? In my application I'm prioritizing privacy and security.