Splitting a PNR - any dangers?

I have (after some battling) got flights I want for me and the Mrs as follows:

NYC-IST-MLE-CMB-SIN-NRT-NYC

Unfortunately due to several equipment changes I lost my I class seats and am stuck in X. Flying on Turkish, Singapore and ANA for these.

I am waiting away for 2 seats to open up and I think in vain, but I think that 1 might, then another may or may not later. Therefore, if I confirm availability in X for this itinerary is in place and then call to split the booking into 2 separate tickets I think I might increase the chance of one or both of us getting into I class, the most desirable I being the NRT-NYC Leg.

If I split, are there any dangers - I guess I could lose the original seats I have (hence me wanting to confirm on Expert Flyer that there is a buffer first) but are there any other red flags or problems I could run into?

I have no status with UA, any fees to worry about? If the only fee is to change class from X-I (and that happens twice) then I would be happy with it.

Thanks!