So I own every pack for the Sims 4 except toddlers (feel free to gift! lol) and running a beefy high end computer. Having recently installed Seasons+all packs, while frame rate is steady at 1440p without issues, its also using a lot more resources compared to just the base game (more memory, ect).
Now Variety has reported 3 more years of Sims 4 content is being planned (medieval/renaissance world gamepack pls!) and that means a lot more packs to come.
In terms of game performance, that requires serious optimization, but will also present us with a version of the Sims we've never experienced content wise and I think will be pretty amazing if they make the right choices/keep the quality high.
As for the Sims 5, its going to seem bare bones compared to the Sims 4 and there seems to be this general idea it should be open world, include a color/style wheel (i really just want one for hair colors and I WANT IT FOR SIMS 4...um sorry) and have realistic graphics. Basically the Sims 3 with skins/mods, a 2.0 version without the bugs.
If the Sims 3 proved anything all of those features used a LOT of resources! For all those things to happen in the Sims 5, you will need a pretty decent rig just to run the base game at 1080p, let alone 2k or 4k. Then comes the "packs" and I suspect after 2 years the Sims 5 will require a high end computer and I honestly believe 50% of the Sims community are using laptops that wouldn't be able to handle that.
So planning 3 more years for the Sims 4 is both a good and a bad move for what will come, I think its great though if you love the Sims 4.
Plus 3 years is an interesting number considering it end of life cycle for Sony/Microsoft current consoles, meaning the Sims 5 might be planned for the next generation but thats complete conjecture on my part.
One piece of advice - if your computer is having any issues running the Sims 4 at high settings with all the packs installed now, you might want to plan for an upgrade in the next few years to run new packs. Especially if you have any hope of running the version everybody seems to expect of the Sims 5.