Really, unless a message is specifically mentioned in one of Whiting's technical directives as being considered incompatible with Article 20.1 SR, I don't see how they can impose a penalty. In the last part of last season, the teams started off playing things cautiously, then started pushing their luck in the last few races. There were no penalties.
Personally I think this needs a regulation change, because I don't like the notion that Whiting can effectively fire off an email and that's suddenly an entirely new rule. Technical Directives are supposed to clarify what is unclear regarding rule interpretation, to let the teams know how the FIA intends to monitor compliance, etc. But the fact that verbal advice or instruction to drivers over pit-to-car radio was not considered to be aiding the driver for the purposes of the "drive the car alone and unaided" rule was such a well established interpretation, which had been universally applied and accepted without question by everyone for over 30 years prior to Monza 2014, that it cannot in my view be right for it to be changed without a proper regulation change. There is no coherent and consistent interpretation of the regulations as written that agrees with the interpretation laid out in the relevant technical directive, so the technical directive effectively contradicts the regulations.
If you're not going to change the regulations for a fundamental thing like this, why should the FIA ever bother with regulation changes? If you can have a technical directive that contradicts and takes precedence over a regulation, there's no need to ever change a regulation through the proper channels again. We're getting pretty close to that now.
Anyway, I expect the teams to keep pushing the boundaries of what they can get away with until either somebody cops a penalty, or the team radio clampdown is simply rendered moribund.