It's completely reasonable. Amend the lease to stipulate they have to do the same when they move out (and show invoice from cleaning company, or it comes out of their deposit). If they agree, it's all good. If they want it cleaned simply because they want a clean place, they should agree.
I had an allergy attack (cats) once when viewing a property. Place was otherwise perfect for me, so I asked the landlord if he'd have the carpets steamed and the HVAC blown out and offered to do the same when I ever moved out. He refused, said "it's already clean". So I said thanks anyways and left. If I'm having an allergy attack, it's not clean.
I can eat more hot wings than you.