Ageless Music?

Dylan not a great songwriter...........I'm going to lie down............
I think it's impossible to tell actually.
It depends whether there are Rock historians,the level they look into it and it's influence on the music of the day.
You can be sure if Rock history is important then Floyd will be remembered,something like DSOM is a s relevant today as it's always been.
They are selling masses of records thirty years on...not sure the Tin Pan Alley guys mentioned above have managed that....
Dylan has already been studied like no other rock musician and this phenomenon will possibly keep him in the historians eye.
I think it depends how music develops but Porter et al may not actually represent much more than an era.
The Beatles were linked more strongly to cultural happenings than any other band and their unique ability to match critical acclaim with massive popularity has secured their place in history as arguably the icons of the 20th century.
Many of the Classical greats were ignored in their lifetime and indeed many of the popular greats from centuries gone by are forgotten by history............
Unlike SACD/DVDA this is one argument we won't live to see the outcome

publishing and licensing rights will determine music for the ages(at least going forward).

From likes of what you mentioned nothing will survive,I think. Elvis has a chance on this continent and beyond; as do Miles Davis,John McLaughlin,Paco De Lucia and Dead Can Dance in Europe and Asia. Flamenco singers El Camaron and Antonio Mairena will live on forever in Spain.

No music is ageless! Your reference to the classical greats presupposes that they will be as popular in 200 years as now.....but, in fact, interest in classical music in general is waning already. Music is a reflection of the society in which it exists - just as any art form. Sooner or later it passes on to become nothing more than an interesting (or not) historical footnote.

I think the only thing that will always be present in music is rhythm, the BEAT!

Yup, whether a piece of music "lives" on or not depends totally on who is around in the future to appreciate it. Any proclamations about a recordings cultural viability (or lack of it) is pretty speculative, but we all have our favorites. Miles Davis, Can, Captain Beefheart, Monk, Hendrix, Stravinsky, Mingus and Ellington all expanded things quite a bit. Can't see their ideas or recordings a evaporating anytime soon.