I think that is not difficult to add this, but also consider that RCS gives each drivers audio feedback on tyre (4 warnings) and fuel (two warnings) levels, plus there is also the track conditions and weather. What I am saying is that with all these messages played it could make things a bit confusing. But again, if this is going to be provided as an option is up to the drivers/race host.
Myself, I would like to have more fuel levels warning (at 50% and 5%) as for the tyres....