I think its silly to think players would be scared off by having things to do, Especially when the game is designed for you to be able to do it at your own pace.
You ruin your own experience and journey by being scared to commit to it. MMOs, Movie Series, Book Series, TV Shows & Anime Series, and even other Game Series are a time sink. If you want to get to the end and see what the fuss is about, you need to be willing to put the time in, like everybody else before.

I dont personally think FFXIVs longevity is at risk because of New Players having ALOT to do. Its more dependent on if the game Continues to be fun and exciting and offer a good time overall. Either in Content, or MSQ Story. For me...so far, I think this game has a Bright 10 years ahead, as long as they dont make any GRAVE mistakes that would turn off their community as a whole.