This seems to be a rabbit hole that is easy to fall into and impossible to escape from. It seems to me that the current state of affairs is that a part 91 light airplane operator whose plane is not approved for flight into known icing conditions can legally fly into conditions that might lead to airframe icing as long as he has a good plan to get out of the icing if it happens and actually does get out of the icing when it happens and, if anything happens, the pilot will be judged after the fact based on his planning and in-flight decision making. Meanwhile, the operator of a light plane that is FIKI approved can legally fly into known or probable icing conditions and keep going in those conditions, but common sense says he should really be working promptly to get out of the icing when it happens and, if anything happens, the pilot will be judged after the fact based on his planning and in-flight decision making, under the guise of recklessness. The FIKI systems usually have greater capabilities such as larger TKS tanks (Cirrus) or hot plates instead of windshield sprayers (Twin Cessnas). But no deice system on a light plane is unlimited. In both cases, the pilot needs to understand the limitations of his deicing equipment so he can both survive encounters with icing and keep his pilot certificate. Basically, you always have to ask yourself: 1. Based on all information I can get, what are the chances I’ll pick up ice and how bad is that icing likely to be? 2. How will I get out of the icing if it occurs? I actually ask myself those same questions flying my totally unprotected airplane. The answer to #2 is just a lot simpler: stay out of the clouds if they are likely to make airframe ice. So, since the process of planning, avoiding, and getting out of icing is the same other than the duration and severity of icing you can stay alive in, what is the practical difference between a FIKI light plane and a similarly-equipped non-FIKI plane?