I really enjoyed reading (and attempting!) immortal Dynasty stories for the Sims 3 and I was curious to see if it was possible in 4. Sadly, there doesn't seem to be any ambrosia, but there *is* a drink that you can buy for 1500 points that rewinds your age to the beginning of the life state you're currently in, which is similar to ambrosia. The trick is, it's not cheap and you only get one drink per purchase.
My current strategy is after creating a sim and using Pinstars method to move them to the big lot in Willow creek and buy a knight to drop their money to 1800 cash is to move people in! I moved the entire Caliente family in (and they brought a whopping 178 thousand simoleans after selling off their furniture!) and the one sim male I chose to be my founder's hubby. Don and Katrina had a baby boy, and my sim and her hubby had a girl, bringing the house up to 8 inside of a week. My sim is now devoting herself to maxxing a skill, an aspiration, a job, getting 6 best friends and making 2 reward purchases that will be unique to her (her unique maxxed aspiration will provide her third unique reward trait).
Since there are no opportunities, or properties, or paintings to make, I'm attempting to see if I can get all the requirements done *before* elder, as there are some hefty drawbacks to elder activities that weren't around in Sims 3. (Death by whoo-hoo and exercising come to mind right away!)
All those spare sims are busy busy busy generating points to buy potions to be put into the immortal's inventory. I am switching out their aspirations regularly so that they are progressing through as many low level ones as they can, and then back to their 'focus' aspiration to keep building that. The hope is I can front load enough potions in the first two-three generations while there is still space in the household for 'helper' sims to create enough potions to see them through all eight generations of immortality, since the immortals have to buy other rewards at first to fulfill their requirements.
So if anyone else is trying out a quasi-immortal dynasty, I'd love to hear your tips! I can already see that the pure randomness of baby gender means that one cheat to CAS after a baby becomes a child in the 7th generation to gender switch them to girl may be necessary, since there's no way to guarantee one like in 3 with watermelons.