Do game developers plan to start small on a new hardware, to have space to evolve while creating a series of that game?
They most certainly do not!
When I first joined the games industry, I asked a producer from [giant publisher you've definitely heard of] this very question. He told me that every console game his company developed used 100% of the platform's available resources. While this was probably not the literal truth, it's close enough.
If anything, console games spend most of their development using closer to 120-150% of the platform resources. The last few months of development are spent frantically trying to crunch everything down to "only" 100% before the ship date. If subsequent titles need more CPU cycles / RAM / disk space / etc., the developers first have to figure out how to optimize their current technology -- find more efficient algorithms, use better data compression, etc. Thus, rapid evolution by necessity!
It makes perfect sense, actually; what competitive advantage would there be in explicitly not trying to reach the full potential of the hardware, given your current knowledge of the system? Would you trust your competitors to show the same restraint?