I use the same airspace as other pressurised aircraft and I want to know what level they are climbing to. "Flight levels" doesn't cut it. If i'm descending from 370 and some one is climbing to "flight levels" and G airspace starts/finishes at 180 then flight levels may require more transmissions with some cool sounding wally with fantastic airmanship.
You are forgetting this is a CTAF call we are talking about. And we are operating under the IFR. So when a departure report is made on the area frequency, the intended level is included with this call. Then, when you request descent from FL370, centre will clear you to leave CTA on descent, and give you traffic information on 'the dash' including its flight level climbing to. Remember how it works now?