Can't see Saudia releasing pilots to go to RIA, if they do who's going to replace them.
Cadets will happen later but not for the first few years at least and then only in measured amounts.
A320/737 Captains to A350/77X Captain, wishful thinking from aspiring narrow body pilots. From left seat 320/737 to right seat 350/77X maybe. Sounds fine and dandy until until they have their first flight across the poles to ORD in the middle of winter or to PEK for the first time. It was tried before in another nearby airline and they got away with it, just, thanks in no part to the existing demographic of more experienced FOs as well as a well established training and procedural systems in place. Even so the experiment was not repeated.
RIA will not have such a luxury, A350/77X pilots will consist of well seasoned wide body types, not boys from some low cost carrier strapping around their backyard in a bug smasher.