I'm wondering if you could present it in a way that is an exciting thing. As in a graduation to the next steps etc.
We don't do that specifically, BUT we do implement a salary system for the kids and it's different at different ages. The big separation is 6th grade. So under that age the kids get a much smaller amount of money but have a much smaller amount of financial responsibilities. Once they hit 6th grade they "graduate" to the next system. Where yes, it's exciting that they get more money BUT it also comes with far more responsibilities (having to pay for items themselves that we used to pay for). They know that this is what happens at this specific age.
Tying that all back to your situation
I'm wondering if you could implement something similarly. As in, "this is our family situation for under ages x. Once you hit age y you graduate to the next level of priviledge and responsibility!" Insert excitement!
And maybe increase the level of reward that he can work towards.