Let's say you can afford to go in 2018, but like most of us, you'd be happy to pay less. So you wait until 2019 to see what happens. The hunt might get cheaper, but if it gets more expensive, you might just find that you can't afford to hunt anymore, or to hunt as many animals.
I'd suggest that trying to speculate on future hunt prices is like trying to speculate on any other commodity - everyone has an opinion, but it's only yours that counts. If you bet wrong, you can't blame anyone else. And in this case, it's hard to bet right because there are lots of variables. The supply and demand for animals is only one factor; foreign exchange rates - which are notoriously volatile - and government regulations (remember Tanzania and taxes?) are also involved, but there are others.
My advice to someone with this question would be to go when you can, have the best experience you can, and don't look back. If things do get cheaper, rather than feeling like you overpaid, consider that a return just got easier. If they get more expensive, well, you can be pleased you got a deal.
Either way, you win by going now, rather than waiting and potentially losing out.