I'd need to find the post again, but there's a very well known internet bod who has fully evidenced that he has the inside track on BMW releases - been proven over many years. All I can recall is that the 1300 will be released in May 23, will have rear radar, will retain the telelever, will retain separate systems for tft and satnav (will not be a 10.4 RT style dash), and will have auto-lowering like the HD. More importantly, I expect, it will be a whole new chassis and, hopefully will be significantly lighter. Complete re-style as well I guess.
I bought the first of the 1250TBs in late Oct 20 because I was convinced of the upgrade over the 1200, notably the engine but also some of the nice-to-haves. But that was with a 30 mth gap in waiting for the new bike. With a new bike here in 15 months, I'd be inclined to hold on, but it really depends on the deal. Remember, whatever deals are available as we get towards the new release, the price will be reflected in the trade-in/resale, as it will be the older model. You'd take quite a hit to then move up to the 1300.
Stick for one more summer, I'd say.
Of course, if you are coming to the end of a PCP, then paying the balloon might not be an attractive offer on the current bike, in which case, why not try get a 2-3 PCP deal on a TB.