There's also a physical limit to it, as it stands, in order to have a completely non-custodial future in LN, everyone needs to be able to have their own channel. The cost of opening and closing channels will prohibit this as there are just not enough sats to do so. 
That's why I think it's impossible, but we should strive to be as self-custodial and trustless or trust minimized as possible in all the layers we build.