Field 18 is the 'remarks' block always has been always will. The only required information in F18 is DOF and Diplomatic Clearances (if you need them), everything else is supplementary. You could even request your favourite sandwich at your destination in F18 if you really wanted to! The 'RMK/' prefix still wont be computer detectable and if it is it'll be ignored as extraneous information.
On the face of it these changes mean very little to GA apart from the FPL codes are changing; enter what you have on board into the FPL F10a/b (or approximately, providing you can ensure compliance with any potential instruction given based on the aircraft capability). Unless you are flying airways with every piece of kit on the market but without a transponder no one's going to give a s
t!
Edit: More significantly than over complicating an updated SOP to FPL filing, with the removal of ADF from the equipment spec does this suggest a move toward the total removal of ADF/NDB all together?