Neville was assuming that United would be challenging for the title quite quickly, and even winning it. Within a few years. As of between when he made that statement, i.e. spring 2014, and spring 2020, Liverpool are champions, despite the fact that he assumed “it would be many, many years” before they'd even be close. I personally think United are several years off being serious challengers for the title. Next year, despite all the doom mongering today, I can't see beyond us and the dippers (with the proviso that we recruit a couple of good players in the summer, and we don't get these ridiculous season-long injuries, i.e. Kev last season, Aymeric and Leroy this). Nobody in the country outside of Blue Moon thinks we've suddenly become a shit team because we lost to Chelsea and have lost out on the title.
Re. United being plausible title challengers. You never know. Leicester won it, and who saw them coming? Certainly, the media will be bigging them up. As they always do. As they did last summer when the rags beat Chelsea heavily. It sells.