A6000/A100/H100/etc will sell like hotcakes to hobbyists and small companies when data centers start to get rid of them (if they're allowed to). the market is starved for affordable hardware. P40 was <100$ 1.5 years ago, now it's 250$+
To your point on the P40, it's an eight year old card but fortunately Nvidia has a history of long term support (especially for "datacenter" GPUs). The Pascal series is still fully supported by the latest Nvidia driver and CUDA releases, and projects like llama.cpp are still fairly regularly adding performance optimizations for even Maxwell series GPUs!
Current V100/A100/H100/etc hardware families are not going to end up as e-waste anytime soon. In fact, compare used pricing (and demand) of GPUs to CPUs, RAM, disk, motherboards, etc from eight years ago... That hardware ends up in the trash/at e-waste recyclers much, much sooner (even with /r/homelab).