December 2024:
BAE Systems is already developing Striker II under a £40 million contract announced by the UK Ministry of Defence in September 2023 which will see the helmet undergo flight trials in the coming months. The latest investment will fund the next stage of development, ensuring the helmet achieves a production-ready standard. - Source
So, Id guess not in service yet, but has either undergone flight trials or is about to.
Shouldnt have any intergration issues with older aircraft, especially current Striker I users like the Typhoon
Striker II has been specifically designed to allow for easy integration across a wide range of platforms. It’s compatible with aircraft that have analog display drive electronics, via a low latency converter, and has a digital interface for aircraft with digital display drives. Its comprehensive list of features work together seamlessly to provide pilots with unmatched awareness. Most importantly, the information is displayed in an intuitive way, allowing for a natural response in what can be the most challenging and unnatural of environments.
BAE Systems can provide complete HMD System solution using the Striker II, or work with customers to integrate Striker II into existing aircraft architectures on an Open Architecture basis to give customers the freedom and ability to develop their own symbology/display formats, and provide optimized aircraft mounted hardware solutions. - Source
You can see what it looks like in this:
Edit: According the BBC, it has a planned finished development date of 2027
The firm aims to finish development in 2027, with production starting soon after. - Source
and according to this tweet from January 28th, trials have started, including night flights
https://x.com/BAESystemsplc/status/1884315507727196508
Which should be more than enough to get it added to in-game.