Is it worth upgrading to a Ryzen processor from a i5-4690k?

That depends on your goals and budget.

I am a fellow render and modeling enthusiast. I also do some Video stuff (though not very fancy). I use an Intel i7- 5930k which together with the 5820 represent the best hybrid chips for those who don't mind a little overclocking. The 6850 is better for those who run at stock speeds. Those are 6 core CPUs and so have a higher clock speed than the Intel 8 core options. I found that stepping up to 6 cores was a very nice upgrade compared to my previous 4. I have brought some of my stuff in to experiment at work on a server with a pair of 22 core Intel® Xeon E5-2699 v4 processors. (44 cores x 2.2ghz) and compared it to my 6 core 5930k (6 cores x 4.4ghz). Due to decreasing returns the monster server was only around
So in theory a comparison of "27ghz" vs "97ghz". The render times were around 2-2.5 times faster depending on how crazy I went with fancy lighting. The reason was the law of diminishing returns.
The more cores you spread the work over, the lower the % gain.

For gaming the ideal number of cores is 2-4 cores. Some games scale to 4 cores better than others. It depends on how parallel (threaded) optimized their code is. For rendering the sweet spot at where render speeds no longer have a linear gain is much higher. I would guess (no testing of any kind by me on this, just an educated guess) that the render sweet spot is somewhere in the 8-12 range, maybe a little higher for some tasks. My rendering is in Cinema 4d, Lightwave, Poser and Bryce. But I"m fairly certain it would be similar for 3d Studio Max, AutoCad, Maya, etc

The thing is that as you move to a more "pure" version of one or the other compromises are made. A pure render machine is capable of gaming, but not ideal. A pure gaming machine is capable of rendering but not ideal. In to this mix you have to throw budget as well. If rendering is more important, then you splurge on a multi-core CPU and put a bunch of ram in your PC (32-64gb seems ideal for most, except for the consumer grade ones like Bryce, Poser etc which do fine on 8gb or less). Then with whatever you have left in your budget you get as good an openGL video card as your budget allows.
In that I wanted a hybrid, my graphics card is not a Quadro but a 980ti.

So where does this leave the Ryzen and your question?

That depends on what you want and what you are willing to spend to get there. If gaming is your main goal, right now most games are not well optimized for multi-core and so the fact that these new AMD chips have more cores than anything close to their price point is very important. What is important that with the same amount of money spent, an Intel system will (for now at least) give you a faster gaming rig. If on the other hand you're willing to give up ~5-15% frame rates in games for 20-40% faster renders then the Ryzen system makes sense.

If you are not strictly focused on ROI (return on investment) or on keeping the cost as low as possible, get an Intel 6+ core system.

So I didn't answer directly if it is worth it; that would be up to you and your wallet. To me the Ryzen seems an amazing low cost render option but does not seem ideal for games yet. Where you fall in the spectrum of gaming vs rendering only you can answer.

On a side note: only an idiot would try to play games while rendering. Pull up task manager and look at what rendering does to your CPU. When rendering, consider your PC to be busy and let it do it's thing.

For some very interesting early reviews of the Ryzen look at Anandtech's and Arstechnica's reviews. Well written with differing points of view.