This forum has done me a great service in ensuring I don't set foot on a dreamliner in Economy class unless absolutely necessary.
I've experienced 10 across in a 777 and it was dismal. The journey was undertaken due to work travel with a strictly Y policy and I will do my utmost to avoid that aircraft in economy class for personal travel. Hopefully the 77X features a wider body so that an appropriate seat that doesn't cram everyone is fitted. Pretty sure the 10 across 787s have the same seat width in 9 across.