I don’t really know how RAM gets allocated. If a new OS supports greater background/multitasking, would current programs be able to eat up more RAM, perhaps over 8GB?The only reason you’d need more than 8GB of Ram in an iPad is if it was running new programs; not currently available. If you design new programs for something that requires more than 8GB of Ram, your market is very small(only 1TB and over 5th gen. iPad Pros).
I would say, keep the 600 dollars, and wait for what comes next… buy devices for today with the chance of a good tomorrow… Don’t plan on the future… and that 600 dollars can grow way more than the 8GBs of extra Ram in your iPad.