I do not like any "retrofit", as it involve many technical challenges to solve "impossible", what result into for me not acceptable compromises: Light quality, reliability, safety, cost, efficacy, to name few of them.
And why? Because somebody think "It would be costly to replace whole luminaire"? When the LED based retrofit lamp cost more then ten times the incandescent fixture they are intended for? Why i have to pay for "special phosphor coat technology to allow more even phosphor thickness on spiral shaped lamp", when on stright tube the way more even phosphor distribution is a piece of cake?
Don't tell me, then the purpose build decent LED lantern would cost more then the technically difficult E27 based LED lamp plus the incandescent light fixture, when with porpose build fixture many techical challenges simply do not exist (e.g. limitted space for LED heat dissipation)