If you mean support for new CPUs for more than 4 years, then you're not likely to find that. Intel tends to require new motherboards for their processors every 2 years or so, so I would expect that the CPUs they release next year won't be compatible with their current motherboards. AMD tends to be a bit better about that, and announced back in 2016 that they planned to support socket AM4 with new processors through at least 2020, but at this point, 2020 is already next year. So, I wouldn't expect any new processors coming out more than 2 years from now to support current motherboards. So, if you are interested in updating to one of the latest CPUs several years down the line, keep in mind that you will likely need to replace your motherboard as well, and perhaps your RAM to DDR5. So it might not be worth spending a lot on a high-end motherboard.
On the other hand, year-over-year improvements to per-core performance of CPUs haven't been all that large for quite a while. In fact, aside from adding more cores and threads at each price level, current processors are not massively faster than what you already have. A 4690k is still a very capable processor, and is about on par with the current quad-core i3s. Some games are starting to benefit from having access to more than four threads, but a quad-core should still run fairly well in most titles. Unless you are interested in improving performance in certain heavily-multithreaded games or applications, it might be worth focusing on the graphics card upgrade first. Or perhaps wait until AMD and Intel launch their 7 and 10nm CPUs later this year, and upgrade the CPU and graphics both at the same time.