For the record I am not AMD fanboy, I had Nvidia GPUs for around 10 years. I just realized the plans and the whole concept of Nvidia, which is something beyond evil.
Just so you know, the only reason AMD is even still a company is because Nvidia and Intel let them, so that they do not hold monopolies. AMD truly still is the option for budget systems and the performance they can have is amazing for the price. Regardless, AMD software support is so behind the times and its something that has always plagued them. Besides, I'm fairly certain being on Unreal 3, almost nothing TWI could do would max out your R9 290x even with all the maxed settings.
As far as certain visual effects only being possible with nvidia, well, its a hardware level thing. Such things simply are not possible on AMD cards, or if they are they bring the card to its knees because it wasn't designed for it. You really truly do get what you pay for when it comes to GPU's and CPU's. Maxwell architecture makes the 900 series capable of being produced extremely inexpensively, compared to the 700 series cards while still outperforming, and using less wattage / perf. Tesla on the GM200 is going to be something to behold. I'm interested to see what AMD will come up with that isn't "COOOOOORES".
But yeah, on topic if you want those effects you'll have to pressure AMD to do things to support such effects, then get TWI to work with it. Ultimately its AMD's downfall for not having it, not some evil plot by nvidia. Theres nothing wrong with wanting to be the best and thats what Nvidia is doing, they're not letting anything hold them back.