As you know, rubber trees now only drop about 1/2 sapling per tree. E.g. you cut down 10 rubber trees, but only get 5 saplings. This is so you can't grow rubber trees, cut them down for their wood, turn that wood into rubber, then rinse and repeat, but instead have to keep live ones that you extract resin from (which is more realistic). This is fine by me.
The problem is that this also means you can't expand (or relocate) your rubber tree farm. You have to make do with whatever occurs naturally. Unless you build your base in a swamp biome with plenty of rubber trees, this can make rubber trees a very rare resource to come by. (Especially since they're hard to distinguish from other trees.)
My suggestion: add a small chance (e.g. 10%) of getting a sapling when you extract resin from a rubber tree. This would make it possible to slowly expand your rubber tree farm by extracting resin like you're supposed to, without making rubber trees "exploitable" like they used to be.