I don't think it really matters whether we buy Sims 4 packs or not. When Project Rene/Sims 5 releases, eventually support for TS4 will end. It may be 6 months after release, or a year but it will end.
When TS4 came out, TS3's support ended shortly after. Sure you can still buy stuff from the Sims 3 store even today but there are still bugs in that game.
Simmers not buying Sims 4 packs will only make the game end faster. If there isn't any money coming in, there isn't any to spend on making packs.
I won't be buying Sims 5 on release because I'm still enjoying Sims 4. When Sims 4 came out I bought it on release and it sat on my computer collecting dust for months while I played Sims 3, because I didn't like it at first. I love it now, flaws and all.
I also don't want to sink a lot of money into another game, and play the waiting game for specific features. I was naive when I switched from TS3 to TS4, having only ever played TS3 at that time. I have 3 complete games on my computer, no need rush to Sims 5.
And if TS5 is in fact going to be free to play, with microtransactions (as @ryouma17 speculates), I won't be playing it at all. I'll either move onto Paralives, Life By You, or find something else to do with my time.
