That's a misnomer. Old clients cannot validate the new transaction types at all and will blindly think they're valid. This is the equivalent of your browser ac

That's a misnomer. Old clients cannot validate the new transaction types at all and will blindly think they're valid. This is the equivalent of your browser accepting any single SSL certificate that says "X.999" irregaddless of if it's signed. Instead of your browser saying "I don't know how to validate this certificate, please upgrade me so I can". -- Bitcoin core has for better or worse grown synonymous with Blockstream. A majority of commit access holders are employed by them, and unsurprisingly they tend to all vote in a bloc. The roadmap does mention the lightning network, just as a reference to "off chain solutions". The two main issues with lightning are: 1) centralisation pressure among hubs: The number of jobs will eventually converge to a small number of central nodes. 2) Lightning is being developed by a single company in essentially-private, in contradiction to how Bitcoin development has been done since its inception. They refuse to accept outside contributions and only pay lip service.