The primal battles are already catered for casual play as it is because the retry/re-entry timer is so low. A majority of my LS is players that can only play weekend evenings and we still get a lot of mileage out of the Ifrit fight because the prerequisites are easily soloable and it's easy to schedule the actual fight and deal with people coming and going. There is bound to be groups like my own on other servers that are occasionally 1-2 people short so stick a note that you're up for whatever fight in your search comment and set your flag to Seeking Party.
As far as solo content, I'd prefer for more unique solo content instead of just weaker versions of content geared towards party play. Stuff like Company Leve NMs and things like that.
As far as not being able to commit to a linkshell I suggest to party up and find some good people to hang out with. There's more than enough good people out there that will try to accommodate your schedule if you're polite and such, I know I would.
