Eventually (probably next year) we will have them available seperately. However, for most people it makes more sense to sell their old shelter and switch. If you get the new version, you can easily sell your used original version for full price since they are sold out and in high demand. I've seen our $300 X-Mid 2 selling for over $700 on eBay - so you get a new shelter and sell the old you get the preferred version and a new shelter for little out of pocket cost, whereas if you bought just the inner it would cost $100 or so.
The v2 version of the X-Mid 1P launched this spring has added connections between the inner and fly at shoulder height, so if you use a 2022+ inner in a 2019-2021 X-Mid 1P then you can't use those connections which add a bit of shoulder room. It works but not fully. Also, the June 2022 onwards X-Mid 2 is an updated design (shape) where you could fit the new inner into the older fly but you'd likely need to fine tune the length of the adjustment cords to improve the pitch.